^^^^
I'm really sorry to be reading of such problems but, unfortunately, I'm not that surprised.
It's generally known (unofficially) that the Germans build big strength 'tolerances' in their engineering which allows a good margin of 'headroom' for modding/tuning. However, in upgrading the GTI to the Ed30, they didn't upgrade the DSG or manual gearbox AFAIK. And so the 'headroom' has been significantly reduced and hence greater potential for problems in plus-300 territory unless other components like clutches are further modified.
VWR's 330 bhp demo GTI (not Ed30) has a competition clutch and I must say I thought I'd have difficulty with it but it's a pussycat. The short-shift gearstick is trickier sometimes, but that's just me not being used to it yet.
Perhaps VW thought that us English wouldn't be mad enough to mod the Edition 30!