I fixed one of my MP7 mags with some instant gasket maker, smeared on a load left it to dry for 24 hours with the rocket valve removed and it's been fine since. Only had one mag leak since I bought it in January 2013.
Without doubt the TM MP7 is my best gun, for £300 it's range and accuracy are phenomenal.
Gas wise I've been running it on dry propane, no added lube at all. Abbey maintenance gas for storage, I'm pretty sure that's what has kept it going. They're very low maintenance for a gas gun, I have only lubed the bolt once since I bought it and it's running just as well now as it did the day I got it.
Externals wise there's not a lot you can do, FMA make a copy of the wilcox rail for it which replaces the folding foregrip with a bottom rail. Outside of that I recommend replacing the stock TM flash hider with the nineball steel one, it's a lot tougher and it looks much better than the shiny pot metal stock one. For a torch the element M300 looks nice, or an X300 but I don't think you can get a repro tail switch so you'd have to get a real one (which I heartily recommend, 500 real lumens is painfully bright!)