My 16 y.o. son bought his first car last week. He bought an ''89 Lesabre T type. Its the car his mother drove when he was little. He paid $500 for it, knowing it would need some work.

That''s it the day we brought it home.
The passenger side door wouldn''t open. The previous owner suggested replacing the latch because it was all rusted and gunked up because they never used that door. With much difficulty, I removed the interior panel and was able to get my hands on and open the latch. I called my local Buick dealer to find that the latch is no longer available. Are there any sources for a replacement? Maybe I have to do a thorough cleaning and lube and hope for the best.
I''m a Buick rookie, all help is appreciated.