I'm finally being forced to remove the prechambers on my 300D and I have a question about something, hopefully it's an easy answer...

I know about the threaded ring that secures the chamber to the head and I know about the injector heat shield between the nozzle and chamber. Is there a seal or crush washer or...something between the shoulder of the chamber and the cylinder head?

Yes.

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CENSORED due to not family friendly words

No, they only thing sort of like that are spacers that are used after the entire cylinder head parting surface is machined flat because it is measured out of spec.

That reduces the cylinder head overall height causing the prechamber to protrude into the combustion chamber and potentially interfere with the piston at the top of its stroke. The correction is to through a combination of removing material at the shoulder and installing the correct spacer return the prechamber tip to the correct position.

OM 615/6/7 engines sometimes have a seal as you describe but not the OM 60X engines.

^x2 There is no sealing ring on the 60x engines. Why are you pulling the prechambers?

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

They're carboned up and leaking compression, I've tightened the ring up a few times and each time it did less and less to "fix" the problem.

I'm torn between just pulling all of them, cleaning everything really well and reassembling or just biting the bullet and replacing them all. I'm mostly torn because I'm seeing some possibly conflicting info on the internets about the part number I need. Both part numbers I've seen are 601 numbers but the last 4 numbers are different. The problem is the price difference, one is like $45 and the other is ~$165. If I knew the cheaper(still a factory part though) chambers were correct I'd just replace all of them.