• GST advice on used-car buyback tax treatment

I had a Hyundai Creta under a 48-month novated lease/lease-to-own arrangement with a leasing company. At the end of the lease, they have offered me the option to purchase the vehicle as the end user. They have issued a revised proforma buyback invoice charging CGST 20% and SGST 20%. So effectively 40% total GST on the buyback value of a used vehicle.

Their explanation is that due to post-2025 GST changes, the current GST rate for this category of car is 40%, and since leasing is treated as a supply of service, they are applying that logic. My issue is that this is not a lease rental invoice, it is a buyback / resale invoice for a used car.

My questions:
1. For end-of-term buyback of a used leased car, is GST charged as sale of a used vehicle?
2. Should GST be 40% total, or 18% total?
3. Should GST be on the full sale value or only on margin?
4. Does the novated lease structure change the GST treatment of the final buyback sale?
5. What notification / circular / provision should be checked?

Looking for a CA / GST expert’s view on whether this tax treatment appears correct.