That’s ridiculous. I’d recover the car to a capable ///M specialist.
I think you should open negotiations with your current garage by refusing to pay since they’ve not fixed the problem. Ultimately, paying 50% of the cost to change the bearing shells would be reasonable as it’s preventative maintenance anyway.
Give Phil a call if you’re not too far away:
BMWZ4MC wrote: ↑Sat Oct 14, 2017 12:30 pm I'm in the followers / cams camp. The good news is that the primary failure seems to be the case hardening on the followers, so catching it early and not driving further avoids damage to the cams. If that is the cause, Schrick sell OEM followers to which they apply an additional hardening process. They aren't terribly expensive although I would replace them all. If you need news cams, they are pretty costly and the labour required increases significantly due to the limited access in the Z4M (cf the E46 M3). The job can be done without dismantling the entire front of the car but only by someone who knows what they're doing.
Where are you based? Phil at CPC in Amersham has done this job on several forum cars and many M3s.