Something I told my stepdaughter yesterday. In snow drive very slowly and it might add 20 mins to your journey but at least you'll get there. Rush and it will end in tears.
After reading everything that you've checked, I think it is the driveshafts being different lengths as that was in my head before I started to read the post. Unless somebody knows anything else I think that's the only answer. Is it under gentle acceleration as well or just hard?
Some seat manufacturers do car specific ones. I just googled it and came up with a Corbeau one but sure the likes of Cobra/Sparco do them as well. Just depends whether your seat will fit nicely onto them.
Very tempting mate, I'll have a think as you're a bit far and not 100% on cat c and door. If it was just track then I'd have it but I'll bear it in mind cheers.
No I get where you're coming from but it's the bends that I get the buzz from and to spend an afternoon stripping it to bits is a bit extreme for me but fair play if that's your thing. Plus I'll probably have the missus next to me screaming to slow down anyway at first lol.