DAE use a cheap grease pencil to mark hardware during teardown?

Last week I was pulling the cowling off a 172 at our hangar in Tulsa and probably dropped the same 1/4 inch screw three times trying to keep track of where it went. I got so sick of it that I grabbed one of those .99 cent grease pencils we keep in the bottom drawer and started drawing little arrows and numbers right on the firewall, like "1" for the top left bolt and "2" for the next one going clockwise. Took me maybe 20 extra seconds to mark everything up, but when I put the panels back on it was the first time in 6 months I did not have to guess which screw went where or fish around in the belly for a dropped washer. The pencil wipes right off with a rag and some alcohol, leaves zero residue, and I did not scratch anything. Only thing I am not sure about is whether it could mess with paint or primer on some surfaces if you leave it on too long. Has anyone been doing this for a while, and is there a spot on the plane where you would never mark with a grease pencil?