Wow, makes me glad i have an SEL instead of an SL.
Steve, if one were going to pull the heads anyway (on say a 420 or 560 SEL) wouldn't the only additional components be the hydraulic pump (560) and a/c compressor, with no need to loosen the upper oil pan to r/r the timing cover. In shop time that's 3 hours +/- in labor and expensive to your customer, but for me to add 3 hours to a job that took a month and $10 for the lower rails, it would have made sense "while i was in there"--even if i hadn't found part of the lower left rail in the oil pan. I'd prefer never to do it again, but i am glad i did it once and it worked all right.
You are absolutely right about the a/c compressor, and its carrier, what a PITA.

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Earl McLain
'02 C230 Kompressor
'89 560 SEL "Frau BlueCar" (retired April 2004)