More likely that the valves will go tight pretty fast rather than one breaking -- I've never heard of an MB engine "dropping" a valve (ie the tulip snapping off the stem).

What will probably happen is that there is quite a bit of crud on the stem of the valves that were too tight, and it is holding them open. It will wear off pretty fast, and the clearance will vanish again.

I'd do another valve adjust in about 5000 miles. If any of them are tight again, have him leave them with more gap than specified, then repeat the adjustment in a couple thousand miles. This should take care of it.

The real problem with letting the valves go that long is that the exhaust valves tend to erode very badly when they don't close properly, and they then refuse to seal when the clearance is correct. The only way to fi that is to do a valve job, and you almost always have to replace the exhaust valves then, since they will be too worn to grind.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!