Since, the Chevrolet UVA is 2008 model and driven approx. 85,000 kms in CNG fuel then we would not recommend you to go for that vehicle as the engine is not in its full flow and it may cause discomforts. There are several reasonable and lucrative offers available on used cars on Cardekho which are worth giving a sight. Here's the link: -
The cost for the right side front door is Rs 20,500 and the cost of the rear door is Rs 16,500. Plus you would also have to shell out an additional Rs 8,000 for the denting and painting job. That would bring your overall cost to around Rs 45,000. You can also check with the local service center and find out the exact pricing for this job.
The best engine oil for you car mostly depends upon the engine condition and total running. It is recommended that oil change should always be done from authorised service station. We called a few service stations for you and no one recommended 5W40 grade for Aveo- UVA, so please contact your nearest authorised service station.