Had a bad service experience at a dealer, left with oil/grease stains on my headliner. Any suggestions on how to clean? What to use/not to use, what to do/not do? Thanks~

same thing here, dealer cleaned it for me

GM sells this foaming Leather, Vynil and Upholstery cleaner that comes in a spray can with a nozzel that looks like one from a spray can of whipped cream. This stuff is AMAZING! And will take any dirt off the headline, or your mats, seats, carpet, etc. It was $6 Canadian from the parts department so probably a couple of bucks cheaper in the US. Try this stuff out, it'll take it out no problem.

i had it when we picked up our car new the dealer cleaned it for me

3M makes an adhesive cleaner-strong but safe enough to use on the headliner. Pour a few drops on a 100% cotton terry cloth towel and lightly rub the stains. They will come out. The adhesive cleaner comes in a red and white metal can-many GM dealerships carry the cleaner.