Thanks for the guidance and suggestions!
Timing chain, rails, steering linkages, radiator, belts, brakes, hoses, shocks, etc. all well maintained.
My rationale for turning more significant jobs over to "the Mercedes folks" is based on a few disappointing experiences I've had using recommended independent mechanics who supposedly "really know their Mercedes..." (No doubt there are some top notch pros out there, I'm just not interested in feeling like a damned guinea pig.)
I do tend to use these good local mechanics for procedures I generally understand. When it comes to more complex engine work (i.e. the transmission, timing chain), where my knowledge is limited, I feel less comfortable relying on these independents. "Knowledge is power," and when I haven't got the foggiest idea about what's being done to my car, I pay up for the piece of mind a Mercedes authorized mechanic gives me.
Regarding eBay, I'm a real believer in the feedback system. Specifically, I would never slap down more than a modest sum if the seller didn't present with impeccable feedback ratings. As I see it, I'm at least as safe buying equipment from someone on eBay with huge positive feedback scores as I would be trusting a local mechanic on the basis of a few neighbors' opinions. Maybe it's naive; but thus far, my experience buying auctioned replacement parts for my Benz has been VERY positive, and I've managed to maintain the car in like new condition without breaking the bank.
In any case, I genuinely appreciate your speedy responses to my inquiry. Many thanks!