Hi guys, just an update ... I've been very quiet!
Car needed a bit of work and my expert had identified some future work that needed taking care of as well, so I decided to get absolutely everything done before I start using the car to future-proof it!
So far:
Both rear springs were broken and have been replaced
Water pump replaced
Brake/fuel/EDC lines all replaced (they broke on me on my 2nd spirited drive - a proper shakedown

)
Back axle removed - some badly fitted bushes that needed replacing. They also caused metal on metal contact at the rear and it was badly corroded - this has all been properly sorted and waxoiled
Everything steam cleaned
Interior professionally valleted (alcantara was a bit dirty)
Cat pipes replaced - they did not have a central collector so the lambda sensor was only working on one half of the 3-1 manifold, hence lumpy idle - new decat will sort
A little bit of welding at the front of the engine - a crack had appeared in something (I've forgotten which) which is fairly common
New clutch master cylinder (old one was leaking)
Get it back next week and can't wait
This M5 ownership ain't cheap, eh?