here's a solution...just go buy a brand new M3
If it has become that much of a problem and people won't respond, chances are, they don't know and they don't want to BS you. Check the compressor, the final stage unit, the freon charge, fan motors and all that other stuff and it still doesn't work, then it may be safe to assume that you just need to redo the whole works of the AC system...not a pretty project on the wallet...
yeah I know I deserve a