Clocked or not, 10 owners in 7 years suggests this is a car with issues.

Agree...and would be more than enough to make me run away from it..very fast.!

General question-Even if there were no potential clocking issues and the car seemed a good "runner"-what would be a reasonable sensible monthly maintenance standby budget ?

The full purchase price of the car… it could write itself off in an instant.

Not monthly surely?!

One of my friends runs a 530d, it's about ten years old now, he's had it since about three years. I assume it's basically the same engine, maybe to a slightly different level of tune. It certainly hasn't been reliable, problems with EGR and turbo hoses I seem to recall, engine going into limp-home etc. More recently the indicator failed, several hundred to sort that out as it's a LED unit. But he likes it and generally won't hear a bad word about it, I can sort of see the appeal when he's driving and puts his foot down hard to release those 300 horses. You need deep pockets and don't expect Japanese reliability because you won't get it but I can see why people are attracted to them. Not for me though - I cringed at paying £2 recently for a new bulb on the old Focus...