Im not the only one in germany who have to handle that problem. Some race friends of mine, have the same problem :-(
I've already asked for steel gears to solve this problem and I've been told it isn't a problem. Whether it is or isn't, steel gears would be a nice option (I haven't experienced this myself, but I've talked to several people who have).
My gear boxes are shimmed like crazy. I got the mesh as close to perfect as I could and there is zero side to side play.