Hiya Natalie,
Yes, having the valves set by a pro is a good idea unless you're very handy with a wrench.
But you'll need to specifically ask her to check chain stretch, as most don't do this. It takes an extra 10 minutes, tops. If the chain is stretched 4 or more degrees, it should be replaced. Some say it's OK up to 5 but I'm more picky.
The MB a/f is available at the dealer, or some Internet parts places like *************** or possibly FastLane & PartsShop. When ordering filters & other goodies it doesn't hurt to add a couple gallons to your order, as the local dealer's price MAY be exorbitant (check first). I have never owned an MB with self-leveling so I'm not sure what hydraulic fluid is used, or if you must use MB fluid.
As to synthetics, like I said, there's some raging debate on the subject. Rather than get into an oil war here, try searching this site, there have been a few recent (and LONG) threads on the subject. Bottom line is synthetics don't
create leaks, but they may make them more visible if you have a bad seal etc. In some cases, they can actually stop leaks, as at least the Mobil-1 products have some seal-swelling agents. It can take thousands of miles with synthetic to get the full benefit, and a lot of folks chicken out too soon. Another benefit (IMO) (besides the cold starting improvement & turbo protection, to name a couple) is the ability to use extended drain intervals. I'm doing 10-15kmi on Delvac-1, backed up with oil analysis. Most folks aren't so anal and just go 7.5-10k without analysis. If you use dino oil, make SURE you use a top-rated diesel oil, the best are Chevron Delo-400 and Mobil Delvac-1300, both are 15W-40. If it's not 15W-40 oil, it's not heavy-duty diesel (dino) oil!
Oh, on the tranny, it depends on the car's life. A car that has mostly highway miles can have the tranny last a LONG time, 300k+ isn't unheard of. One that's all city driven can die in less than 200k easily. If yours shifts OK, don't worry about it, but normally 250-300k is the upper limit on longevity. Maybe you got a good one! I agree with your neighbors, these are getting VERY hard to find *in good condition*. Definitely keep yours and take good care of it! (And I think kissing is allowed on the board, at least on the cheeks...
just don't tell the moderators!)
Regards,