The N90's are the notorious backs. I regularly use an FG, an 8008s (and an 8008 with a polaroid back) - the N90 is the only one that's gotten sticky.
It's not that hard to fix though - I used rubbing alcohol, laid strips of Saran wrap over it to let it soak in, and scrubbed with an old terry cloth. That coating is actually clear, so the back stays glossy black. You do lose the Program icons (I don't think that body ever left "M" mode though). It will come off easily where hands have touched it over the years; the rest will still be visible but not sticky, more like you rubbed a clearcoat halfway off. I gave up at that point, but it seemed if I kept going or got out the 99% alcohol I could have finished the job. I just wanted it not-sticky, not concerned with looks on this body.