OK; Well I welcome your inputs - and take it all under advisement... Am particularly encouraged for yet another reinforcement that these engines will survive to high-mileage old age. This is my goal!

More data: Car's oil changes have been good/frequent. Runs/ran! beautifully - before it started misfiring. PO told me it consumes a bit of oil, but was not very specific as to quantity... Obvious oil leaks around cover gaskets. In addition, bit of oil smoke on startup and acceleration from dead stop. At 172k, stem seals seemed like an easy - if perhaps partial - answer.

Few plugs I've pulled out to inspect. One was pretty fouled, and did correspond to occasional misfires on that cylinder. Others/all are 'gap-burned' to pretty open gaps. With two per cylinder, I'm guessing there is still 'pretty good' firing. Is plug replacement overkill in such context?

I did swap positions on two coils, with no clear resolution.

However, misfires are 'floating - and I see no evidence that camshaft position sensor has ever been replaced. This also seems like an obvious culprit. Starting with that.

Thanks for feedback, guys. Happy to hear more...

PS - I would argue that my Diesel 617 engine is the best they ever made, but a topic to discuss over a beer!

__________________
'83 300 SD
'05 E320 4Matic
'06 BMW 530 xi
'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr