To answer your questions:
1.) Yes, these leaks are very common issues on that engine (M276) even without high mileage. There is a
TSB for these leaks.
2.) If you are comfortable/familiar with basic engine repair work, then, yes, this is straightforward. I don't have a URL link to instructions/videos for your specific chassis-engine combination, but someone else might be able to help you with the details. You will want to do a very good job of cleaning the mating surfaces before re-sealing them with the Mercedes-Benz-recommended sealant. Also, it is advisable to replace the intake plenum flange gaskets/"donuts" before putting it back on. There is one other issue to be very careful about, which I will get to below...
3.) That quote from Mercedes-Benz is fairly close to what the Mercedes-Benz dealerships in the Greater Boston area would charge for that job. Your bill might end up being a little higher, since the estimate/quote seems to be missing a few parts and supplies for the job... A 2015 ML 350 (M276 engine) that we purchased pre-owned last year from a dealership had a leak from the front timing covers. Their Mercedes-Benz service dept. had performed the repair for this a few days before we purchased the vehicle. I asked to see the complete invoice, which they provided to me (see the attached image), and discussed the work with them. Although they weren't leaking, they usually also replace all of the camshaft adjuster magnet/solenoid O-ring seals and all of their bolts when they address the front timing cover oil leaks (see the corresponding line items in the attached invoice). They also said that they checked the connectors to the engine wiring harness and that they did not find any oil seepage. This is important. A common issue with the M276, M278, and several of the earlier Mercedes-Benz engines is that oil leaking from the camshaft adjuster magnets/solenoids, as well as from the camshaft position sensors, can get into the engine wiring harness from the connectors and travel through to other sensors, components, and even the ECU... This serious issue is discussed in
this video. What caught my eye is that the technician reported in your quote that one or more camshaft adjuster magnets/solenoids were already leaking. I would verify this with that shop and find out whether they also checked the connectors to the engine harness, other sensors, and the ECU for oil intrusion via the engine harness. If not, then this is something that you or your technician must do. If it is indeed the case, then I would heed the advice in the video that I shared. You are going to have to clean out the connectors and components with electrical contact cleaner. I would also replace the camshaft adjuster magnets/solenoids (the newest revision has a new Mercedes part #) rather than just replace the O-ring seals. I recommend installing the adapter wiring harnesses for camshaft adjuster solenoids (i.e., Mercedes part#: A2711500156...what some refer to as the camshaft adjuster solenoid "pigtails" or "sacrificial harnesses") between each of the solenoids and the engine wiring harness connectors. Although these components were specified for the earlier M272 and M273 engines as part of Service
Campaign No. 2012070002, they are also compatible with the camshaft adjuster solenoids for the M276 engines. There have been efforts by owners and technicians to get Mercedes-Benz to issue a revised service campaign or TSB for this specific issue in newer engines, including the M276 and M278, but there haven't been any so far... Lastly, replace all of the camshaft position sensors with the newest revision, as they can also leak oil at any time into the connectors. This is one issue for which owners have to be super proactive. After getting my ML 350 last year, I had my independent shop's Mercedes master mechanic check all of the camshaft solenoid and position sensor connectors for oil (they were all clean), install the camshaft solenoid adapter wiring harnesses/pigtails, and replace the original camshaft position sensors with the new ones. This is the advantage to either doing the job yourself (assuming that you know what you're doing...) or having an independent shop do the work. In my case, the reputable independent shops in our area (Eastern New England) with experienced Mercedes master mechanics are now charging nearly as much as the dealerships, because there is such a high demand for their services relative to number of such technicians around here. It's often still worth it, because they can do extra preventative service that the dealerships might not ordinarily perform (or have the incentive to advise their customers to have done...).
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