M5s may be caused by dead hydro accumulators of the rear shock absorbers - i just changed them both and got "suspn leveling" problem fixed!
I am afraid that there are not so many ways to check these barrels if they working properly, but i've been told that they can't live longer than 10 years (usually).
So the only thing you should know for sure - is the age of your beast.
And now i can adjust ride height of my M5 precisely :M5thumbs:
Good luck everybody :M5launch: