Dear MODs: I did search and couldn't find a thread for this. So I would like to make this a new thread. Please move it to any suitable thread if you think appropriate.
Though this post is mainly about the new online process flow of RC transfer, I thought some background on the sale would be apt to include here.
Finding a seller
After 3 years of trustworthy relationship I had to bid Adieu to my Etios Liva. I am upgrading my journeys to Kia Sonet.
To find a 'Real buyer' was not as easy as I thought earlier. I started the process with CARS24. They did all kind of inspection - including a test drive and paint thickness gauge to find any repainting, and posted in their own auction portal for dealers. And no surprise, prices were 1L below my expectation. I then opted for listing in their portal for general public. Then I started receiving much more closer prices to my expectation.
Meanwhile I posted in Droom (not at all received any offer), Olx (plenty of offers with 75% on low bids and time passers) and then Facebook marketplace (similar to Olx but almost 50-50%). T-BHP classifieds was surprisingly ineffective. Received only one offer.
Found a buyer after 2 months That one was surprisingly from Cardekho - I posted there just incase if anyone sees it. The buyer did a testdrive of the vehicle and was happy with the overall condition of the vehicle and agreed for the quoted price. In fact the day was auspicious for me I guess - because at a time 3 buyers came in and I was in dilemma on who should I finalise the deal with.
Official Sale process
After the test drive one of the buyers paid a token amount on the spot so that the deal is final. The other two were in a mood to bargain more and I was not

I had it cleared in my sale ad that I would deliver the vehicle only with RC transfer completion, which I asserted to the buyer again. I did that in a confidence that my cousin got a hold of an RTO person who helped out when he sold his vehicle. But unfortunately (rather fortunately, because otherwise I wouldn't have known this complete process and shared here) he was not available due to this Covid restrictions and I was shocked thinking that I am going to take a tour of the RTO offices since that day. The first thing I did was to check here for any thread and found a similar thread of RC transfer in Bangalore and got an idea about the docs required so that I could inform the buyer to prepare. Thanks again to the Team BHP world.
After googling a lot I found the Vahan website process is much easier than the regular in-office, especially during this pandemic because most of the Govt offices are running with just 25-30% of staff.
The portal is quite easy and self explanatory. You can put your vehicle number and it will show the available online services.
From that you can select Basic services option for Transfer of Ownership
It will ask for OTP which will be send to your registered mobile number.
There are two things you need to note here.
1. If you are only applying for Transfer of Ownership, you need to select the RTO whos jurisdiction the buyer's address fall in.
2. If you have a hypothecation active then you can apply for HP removal and RC transfer simultaneously
only if both you and buyer are in the same RTO jurisdiction. If RTOs are different, first apply for HP removal by selecting your RTO and then wait until you receive the new RC without a HP information on it.
Select Hypothecation removal from the Basic Services option and pay the fee (200+25 service charge for smart card in case of Tamilnadu and HP removal is free here). Take a print out of the forms (application and fee receipt) and submit it along with the docs from Financier (Get the NoC and Form 35 from Financier beforehand after paying the due amount) in the RTO office. ** I received the new RC in 8 days **
After receiving the new RC, open a new application in the Vahan portal for the transfer of ownership
selecting the buyers RTO office. Pay the fee online (300+25 service charge in Tamilnadu and additional 200+25 for Smart card fee = 550/-). Note that until the HP removal application is closed by the respective RTO, a new application cannot be created against the same vehicle. Usually it will be done in 2 to 3 days and the portal will show 'Smart Card Generated' against the application status. A new application can be opened thereafter - however, the original RC need to submitted along with TO application to the buyer RTO office. So I suggest to wait until we receive the new RC and its free of mistakes. Because as per the rules we need to submit the TO application within 14 days of sale and the proof sale is this application date I believe. Any delay in receiving the RC will add up to the 14days period if we create a TO application earlier.
I had to visit my RTO a couple of times to see if the new RC printed or not. The portal was never updated if its printed or not; visiting after 7-8 days is ideal I think.
For TO application, the good thing is that Form 29 and 30 are pre-filled from the portal and we just need to download it, print it and get the sign from the buyer as well as put our signs wherever required (For any application though its the similar case). After doing that, I submitted the Printed application (Payment Receipt, Form 29 two copies signed in original, Form 30 two copies signed in original) along with the Original RC, address proof of the buyer, a self attested { aadhar copy, PAN copy, Insurance certificate and emission certificate}.
In my case the Buyer doesn't have a govt address proof therefore a domestic LPG bill and a notary authorized stamp paper to support that, were used. Might be different for other states.
First I went alone but the RTO official asked for the buyer to verify the signature and so I called the buyer to the RTO office (fortunately he was available and within 15mins reach) quickly and we submitted the forms. And that's it

I checked the portal in 2 days after to find the name was changed in the vehicle particulars. He had received the RC in 10 days. It was very easy process altogether with a cost of 550/- whereas some agents asked 2500/- to do this. Everything was completed in 20 days.
This is the docs requirement mentioned in the Tamilnadu state transport authority website.

Option 1 - You can check the status of the application.
Option 2 - you can take the print out of the submitted application anytime from here.
Option 3 - During online payment there are 75% chances that the payment gets debited from the account and its not reflected in the Vahan portal. Check the pending transaction status and you'll find it there. Click the verify payment option and you'll get the payment registered with the portal and the application will be completed then.
I hope this information is useful. Thanks to the central govt too to make this digital and thereby saving a lot of hassle in terms of time and money.