The valve cover cap screws seem to work loose and cause the sleeve/spacer on the fan shroud to depart the vehicle in motion. Then if you are lucky enough to find it the repair is simple, if you need a new spacer then MMC or make one from the pattern you have on the existing spacer that did not decide to leave. I found mine (amazing luck) but I have made two such spacers for fellow M3W owners who were not so lucky.
