What Legal Action Can Be Taken for Not Transferring the RC?

Immediately notify the RTO in writing and by registered post (and via Parivahan) enclosing the signed sale agreement, copy of RC, buyer's ID and Form 29 (seller's notice) and keep the RTO acknowledgement/Parivahan receipt; see Motor Vehicles Act, 1988 (transfer/intimation obligations) [https://legislative.gov.in/sites/default/files/A1988-59.pdf] and the Parivahan download-forms page (Form 29/30). [https://parivahan.gov.in/parivahan/en/content/download-forms]. If the buyer refuses, send a lawyer's legal notice demanding immediate transfer and preservation of documents, inform your motor insurer in writing, and if the buyer remains unresponsive or the vehicle is being misused file a police complaint (Zero FIR/complaint under BNSS Section 173) and attach sale proof and the RTO intimation. [https://www.indiacode.nic.in/handle/123456789/21419]. Case law: the Supreme Court and High Courts hold that sale passes title even if RC is not endorsed (Panna Lal v. Chand Mal, AIR 1980 SC 871), yet courts have repeatedly warned that a registered owner may remain exposed to statutory/third-party liability until records are updated (Anand Sarup Sharma v. P.P. Khurana, Delhi HC; S.N. Shanmugham v. Shankarlal Jain, Madras HC). [https://indiankanoon.org/doc/941834/] [https://indiankanoon.org/doc/203363/] [https://indiankanoon.org/doc/607004/]. If RTO does not act or you keep receiving challans, pursue a civil/declaratory suit or approach the appropriate consumer forum or High Court for directions and an injunction to fix liability on the buyer; seek RTO endorsement/penalty against transferee under the Motor Vehicles Act (see transfer/penalty provisions). [https://legislative.gov.in/sites/default/files/A1988-59.pdf].