six hours to determine you have a broken timing chain seems excessive. I can remove the valve cover in an OM602 engine in about 10 minutes - thats all you would have to do to diagnose a broken chain. If they removed the front timing chain cover and/or removed the cam I could maybe buy six hours. You would have to know exactly what they did to determine if the charge was reasonable.

I have fixed broken timing chains on OM615 and OM617 engines and I can tell you that 25 hours for total labor on that job is not bad at all - assuming they are going to pull the head off. I don't think I could do it that fast and the OM602 engine is more complex than the ones I have fixed.

I think you should talk to the guy that did the head work at 90K miles... Seems like maybe he missed something.

Sorry to hear of your problems - good luck

Tim