We have a few recessed lights with no easy access to the body. In my fight with for air tightness I found that they (naturally) are quite a source of air leaks. For those where I can reach the body I just patched all holes with Scotch tape (and I use halogen lights in them, 15 Watts, so they are not hot -- a lamp which was on for a long time can be hold with bare hands, so there's no danger of overheating).
I just wonder -- has anybody seen some clear covers for recessed lights (glass or whatever) to cover from underneath those where I cannot reach above them?