I was recently corrected that the proper statement is, "the most expensive [old/used] Mercedes is a cheap Mercedes." Which is very true, as discussed above. Best to find something well cared for with at least recent records (hard to find anything these days with records back to Day One). As to the W123 vs W124 debate, I rambled ad nauseum in
this thread about that, I'll not repeat everything here, suffice to say you couldn't pay me to own another W123. I've owned several W123 diesels and multiple W124's with both gas & diesel engines so yes, I've had first hand experience with both, over many years.
That said... the factory service manuals are available online from Mercedes for free at
this link, click MB Workshop Resources, then Service Manual Library. The W124 manual is available online with a much nicer, HTML-based index at
this link. If you can follow instructions and have a decent set of tools, you can do most repairs & maintenance yourself. When special tools are needed, check out the forum rental program.
For spare parts, get a free subscription to the EPC
here, learn how to use it to find part numbers, and then look up the part numbers from online vendors. The forum sponsor (Pelican Parts) has a good selection of brands and competitive prices on aftermarket parts (just make sure to never, ever, buy any Uro, FEQ (First Equipment Quality), or APA brand parts no matter how cheap they are). For parts which are not available aftermarket and only from the dealer (i.e., Genuine Mercedes) you can't beat the prices at
parts.com, however their catalog is awful, you need to search by part number using the info you got from the EPC.
So anyway. You're either looking at a 1987 300TD as the only diesel, or a 300TE/E320. As mentioned above, skip the 4Matic, those are notoriously problematic (although fantastic in the snow when they're working properly). I would not recommend any M103 car for two reasons... first they are underpowered (particularly at low RPM), and second they need a complete valve job about every 150kmi to cure high oil consumption. Which leaves you with the M104 wagons (124.092, 1993-95, non-4Matic). The M104 has excellent power and the only weakness is the cylinder head gasket, try to find a car that has already had it replaced, and you should be fine.
Unless you have a strong incentive towards the diesel (i.e., to be smog exempt in CA, or if you brew your own biodiesel and have a cheap/free supply of VO, etc)... I'd look for a 1994-95 E320 wagon. They will be cheaper and much easier to find. It will be tough to locate a well cared for 1987 300TD at a reasonable price.
Good luck with your search!
