I have a 2001 e46 330ci conv, its pretty similar to the M3, its been a cracking machine, servince intervals are wide and servicing costs have been very low £150 1st one , £250 2nd one ; its just clicked over 50,000miles,
Solid build quality, no problems apart from the wiper fluid container now leaks.
All the write-ups speak highly of them, hold money well..
Any specific questions? I'll try and help..