That's what I meant, Bryan! Thanks! I think Loctite makes some of that, too!
(I HAVE used "Hot Pink" fingernail polish in a pinch, too!)
My dad did that trick on a Cadillac he owned years ago... He bought it new, along with the service coupon book for the regular maintenance jobs. Bring it into the dealer, they tear a coupon out of the book and perform the listed service. One of which was changing the air-cleaner oil (that'll date the car for you folks...).
Anyway, my dad suspected the dealership wasn't performing all the service items, especially the 'hidden' ones. So he put a dab of my mom's fingernail polish on the air-cleaner threads and dropped it off at the dealership. The car came back with the service coupon filled out, an invoice for work performed... and the polish still on the threads.
So my dad complained to the manager that the oil-bath air-cleaner hadn't been cleaned. The manager said they're not required to clean it. My dad then said that the service coupon listed that item. So the manager said if it was listed, then they did it. That's when my dad pointed to the nail polish.... The manager was fuming, but my dad did get his car serviced properly from then on.
