Put the link up for the car your going To look at mate ??

I've had 2 M5's never had a single problem with either and Im on the hunt for another one..

providing they've been serviced had all recalls done etc they ain't to bad yes brakes clutches servicing is expensive but it's a 507 bhp capable of 204 mph so not going to be cheap to run

As for bottom ends knocking if think if it's been devices well you shouldn't have a problem my last m5 is currently on 100k miles and still drives like new

Ideally buy one that's had recent throttle actuators and clutch replaced