I’m looking to replace my 1983 300d (361,000 and climbing) and am considering an r class, likely an early model, and probably with close to 200k. Am I crazy? Can they be worked on without buying lots of diagnostic equipment? What are the major issues to look out for when test driving? Are there any complicated “must do” maintenance items? (Timing belt/chain, etc) I tried finding a maintenance schedule, but the website listed changing spark plugs which I found odd and disconcerting on a diesel.

__________________
'83 300D turbo diesel (334k daily commuter)
SOLD '80 240D 4 speed manual, #2 piston pitted from crushing a 10mm nut. Running it 'till it burns through.
'78 F-150 300cid 4spd od (with my great unkle's original sales receipt)
SOLD '66 Ford P-350 delivery truck (almost driveable)
'49 Dodge B1D (1 ton Pilothouse era truck) not running but all there, candidate for om617 and 4x4 conversion when money permits.