Brake Cleaner will do the job
Brake Fluid would do the trick as well, As long as he wants to repaint his truck. LOL, Cheap people make me laugh.
In my experience people are nice by nature.... if you help someone out they will remember you and will be happy to repay the kindness you showed them. Next time you need some plumbing work done you might find you've missed a trick by not having a favour to call in from the plumbing guy round the corner.