I would say that it is "No Man's Land" (1987) with Charlie Sheen: http://www.imcdb.org/movie.php?id=93638
http://imdb.com/title/tt0093638/
In the opening credits they are replacing parts of a stolen Porsche, repainting, modifying counter, etc.
Here is a capture of the scene showing the VIN plate:

This has been driving me absolutely crazy for 5 years. I cannot find the name of this movie. I have searched everywere on the internet for this. Anyway...

All I remember about this movie is that these car thieves only like porsches. The intro credits show them welding off VIN plates in a shop.

Anyhelp? My guess is that it is made by an independent movie company.

Thanks!