Back to the trans.failsafe, well 'new' mechanic hooked up to obd and he believes its an electrical issue (yes very vague) ...he will look at crankshaft sensor, oil temp/cooler sensor, wants me to drive a few 100 km and pop round so he can re-scan codes (he reset all codes and there were a few but he said just one error on one thing can result in the rest)
as for checking for leaks and replacing the fluid he was well aware of the process and said if trans temp is too high then we go down that route and change., but is a risky process gotta get it right.

Basically he doesn't and didn't pinpoint the issue being the transmission or immediately tell me to change it...

All in all he was more up to speed on things than many others I contacted.

I revert on findings...

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E53 X5 3.0d SUV prod.date 11/2004 eng.variant M57N Europe Right hand drive N