Do it yourself ?
It takes 2-3 hours to take it out, rebuild it at a machine shop, and 3-4 hours to put it back. It is a fairly simple job on the I-6 engine and should never ever cost $3K. I don't know where shops come up with these figures. Put new seals, vlave guides, and valve job, it should not cost more that $400. Let me know if you plan to do it yourself and I'll help you.
1993 190E 2.6
Advanced Diesel Systems Test and Research Engineer