Omegabenz,
I do not have any 'first' hand experience with regrinding and hardening cranks...
I do know a guy that spent a couple of years grinding cranks, including Mercedes. However, he is a little crazy and I am not going to have anything else to do with him.
You did not address the question I asked in the post above...
Since those mechanics stated their experience concerning the cranks and low oil pressure... Did you ask them the reason for that ?
Or is it implied that it is the removal of the nitrided surface which wears out (fast?) and causes the excess clearance and thus loss of oil pressure ?
Does that mean that when the engine is put back together the oil pressure is ok for a certain amount of use ?
What I do believe on grinding cranks is that you want someone who does it all the time... and has a good reputation.
Most fine grinding on hardened metals is done under coolant. Therefore I doubt that the crank needs to be rehardened. If the surface needs to be nitrided or peened that is a different question. There is a lot of difference between affecting the overall strength of the crank and just dealing with the crank journal surface.
Why don't you ask those mechanics more questions about their experience.... for instance, was this one regrinder they were dealing with ?