Thanks for the replies guys.

I did search a bit more last night and found more answers on xbimmers.com which seems a little more active. I have since decided to pass on the 50i we were looking at. Although there seems to be a few who have good luck with them, there are a lot more who have horror stories. I’m not shy of getting my hands dirty and am currently rebuilding an S52 for my e36 M3, but it will be my wife’s car and I don’t want to be chasing issues non stop. The N55 seems pretty stout other than the walnut blasting every 50k and seems to have fixed a lot of the issues the n54 had.