Hi everyone,
Hoping to get some objective insight from anyone with experience on OM642 Bluetec diesels, or Mercedes techs.

My mother’s 2011 R350 Bluetec(OM642 V6 diesel) with 275,000 km has always been serviced exclusively at the same Mercedes dealership since new (purchased by her new, one owner). Even after the warranty ended in 2014, we kept servicing at Dealer, and then continued when the Field Measure was installed and the new warranty was added to the emissions system. All oil changes, emissions repairs, field measures, everything at the dealer.

Recently, it developed a significant fluid leak in the driveway. She took it in and the dealer diagnosed it as a major fuel like leak (the line that connects the left and right fuel rails). They replaced it and claimed it under the Bluetec Field measure extended warranty, saying it was emissions-system related and we had no cost.

The car was returned and engine bay cleaned. The next day, on a road trip to the cabin, less than 300 km later, the vehicle broke down. I opened the hood and found fuel leaking out all over the oil pan. We towed it back to the dealer and Mercedes looked at the oil filter and said there was metal in it and diagnosed it as bearing failure. The messaging from dealer was too bad, it had a good run a 275,000km. My mother drives extremely cautious, the vehicle hasn't been abused ever, and lots of highway miles as my parents would drive the vehicle 600km highway round trip to our cabin most weekends.

Here’s where I’m stuck:

• The dealer says the fuel leak was purely external and could never have contaminated the oil.
  
• But there were fresh fuel streaks on the oil pan after the breakdown — so it still looked like fuel was leaking even after the repair.
  
• The vehicle has had oil burning issues ever since the field measure was installed (dealer always said normal for age, no concern unless leaking externally).
  
• They did not check for fuel dilution or cut the oil filter at the time of the repair — only after it seized, saying there was no reason to. I've been told and have read online that its best practice with a diesel engine showing an external fuel line leak to check the oil for dilution
  
• The service manager insists that even if they had opened the filter then, the bearings were already failing and the same thing would have happened.
  
• But I read that high pressure fuel leaks can cause vibrations, stress, and expose worn injector which can allow fuel to enter the crankcase and destroy bearings fast. Especially on older diesels.
  

If they’d checked the oil for fuel dilution or cut the filter at the time, we could have done an early bottom-end rebuild instead of a full engine swap. But now it’s a $30k engine replacement on a 75-year-old woman’s vehicle that’s always been Mercedes serviced. Obviously not considering this at all, but we would have been prepared to put some money in the car due to my mothers comfort level with it combined with her age and how likely she'll really be driving in 3-5 years. We actually have evidence of being prepared to do this as we put significant money into the ML 63 AMG we own with the dealer a few months ago in changing out the lifters, cams, and head bolts.


My questions:
1- Is this just normal lifespan wear for a well-maintained OM642 at 275,000 km — or does this sound like a preventable failure tied to the emissions fuel system repair? I've read well maintained, especially dealer serviced, OM642 should last 350-400k km?
2- Would an experienced diesel shop have done an oil dilution test or filter check before clearing the vehicle? To me if they had, we would have had the option of executing a repair, or we'd know that the oil was clean and this is completely related to the incomplete fuel line repair. I haven't been able to get any response from dealer as to why there were fresh streaks on the pan when the external leak was apparently repaired.

Any real-world insight would help before I escalate further. To me, it's not sitting right that the vehicle failed so soon after it was in the shop, and knowing the history and care. I know its not a low mileage vehicle, and truly not expecting a new engine be placed in the vehicle. I'm just surprised Mercedes hasn't offered any goodwill or acknowledged that maybe this could have been caught or was due to the repair being done incorrectly. Just want to know if my expectations are fair.

Thanks a lot in advance for any insight or thoughts.