I've had the same problem recently when unpacking older models. Makes me question why we bother to collect them. My problem is not with the paint or overcoat since I switched to acrylics and tamiya white about 15 years ago. The problem is with almost every decal made. They turn brown/yellow after about 10 years. I think the problem is the adhesive under the film. This is even with expensive aftermarket decals and some "real-space" type Alps decals. Is there any way to prevent it, or just build new models every ten years?
Look in the hardware store for water faucet airators that fit in the end of your faucet. They are fine wire mess, and their are some that are domed and have a gasket like rim, that fits perfectly on the bottle for the airvbrush.