Just thinking ahead, is the 300SDL and 350SD/SDL totally different creatures compared to the 300SD in terms of maintenance ?
Is there a huge jump in the cost of replacement parts and availability ?
Is the 6 cylinder comparable in durability compared to the 617.95X engine ?
One more thing - how dependable is the hydraulic suspension found in some of these S-class sedans ?

Just as I'm getting the hang of knowing what to keep an eye on in an SD, it's probably not a bad idea keep a replacement in mind in case someone decides to broadside it.
Also, there are probably some SDLs out there that have 150,000 or less miles with years of good service left in their lives.

Thanks -