My perspective is different still.
1. It seems to me that every shop should have a policy on customer-supplied parts, and that policy should be up to them based on their own philosophy and experience;
2. It seems crazy to me to own a fine car like a 560SL and then take it to mechanics who work on NYC taxicabs and can't even be trusted to order brake parts.
Where are you going to go when you have a real problem - you need a relationship with a real shop and you get it by being an honest-to-God customer.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe