will grease ruin my paintjob?

Grease is bad. But if the "body guys" know what they are doing it will be ok. using wax & grease remover will help. put wax & grease remover on it and let it soak in for about 30 seconds or so before you wipe it off. You really don't want to sand it before you wax and grease remove it, that will just grind it in more. if that's what's been done already then your best bet would be to clean it, sand it, and then reprime it. If you haven't sanded it then just clean (wax & grease) it tell the "body guys" about it. They can always use fisheye eliminator for that too.