A Merc S500 is repaired at the "back street" garage which works on our cars. The owner takes it to Mercedes (90 quid an hour) for servicing, and tells them to let him know if any repairs are needed. Merc do the oil change (which costs a small fortune), stamp the book, then anything like pads, ball joints, plugs etc. are done (with genuine parts where appropriate) for £35 an hour instead of £90.
Some jobs may need main dealers (the only place that could read the ECU error codes on my daily driver C-Class 230K, unfortunately), but in the end, they are all just cars. As said above, the tricky bit is finding someone competent and trustworthy (who knows his limitations).
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