A guy that I sail with has developed a number of trackers over the years and put prototypes in allsorts of cars for evaluation. He stuck it in a colleagues (the Finance Directors) M3 and found that when it went in for a service "which is a major service sir so we'd like to keep the car overnight, feel free to keep the courtesy car until yours is ready" it spent 14 out of the 18 hours that they had it ON THE ROAD! Including a 145mph stretch up the A303 outside of Andover at 2.45am. He only interrogated the tracker after it came back with a significant tappet/valve train noise that hadn't been there and that the garage failed to attend to when asked. If they'd dealt with it then no-one would have been any the wiser.
Needless to say BMW were their usual helpful selves, NOT and despite having all the evidence needed to prove the case the technicians remain employed, the garage remains a BMW franchise and they continue to hold onto M-Tech service status.
On the positive side, he tipped off another sailing buddy of his who is a traffic sergeant at Whitchurch and they had a bumper month!