Just wanted to leave some info for anybody else who has the sticky back problem:
- Since the phone support person couldn't tell me for sure, I sent in my N90s to Nikon's NY service center at the beginning of this year (2013) to see if I could get the sticky back exchanged. They would NOT do a free replacement. I received a letter with estimated charges to replace back and clean/adj. the camera: $200.
(- I finally got someone on the phone from Nikon service after trying for about a week, I said I wanted to refuse the repair, but also complained a bit more to the person on the phone. The person on the phone offered to forward the problem to a supervisor and said I should expect to hear back in a couple days. 2-3 weeks went by, and just as I was getting ready to call them one more time, I received a package on my front porch. The unrepaired camera was inside with an invoice saying that the customer (me) refused repair.)
- Following the instructions described in this thread (and elsewhere), I removed the back and spent about 30 mins cleaning it with isopropyl alcohol and cotton balls. Worked perfectly. The sticky rubbery stuff peeled away and bunched up sort of like a thin film of rubber cement. Back is now smooth black, not too slippery. There was a lot of loose residue, so you would definitely want to remove the back rather than clean around the edges with the camera open.
- I'd read conflicting reports on this, but the little white mode symbols on my film back did rub off (you can still read the markings if you look at the reflections off the shiny back in some strong light).