Yeah let's hope so! She did take it to a bmw specialist a few days before and they said the same thing but obviously they want to charge a whole lot more than my mate will.
My mate checked the engine and could find nothing wrong. When scanning it, everything checked out ok. He even checked all the injector values and they were spot on. No warning lights on the dash either, so everything is pointing to something mechanical, and a fucked flywheel that is all out of balance does seem perfectly plausible. Just a real coincidence that he had one not so long ago with exactly the same problem.
Anyway, it's all booked in for him to do it next Wednesday. The owner also wants him to do the glow plug module as well which should clear those two faults. Fingers crossed it'll be ok after that. I'll update this thread then - hopefully with good news!