I always wondered how is the reliability looking for everyone so far in the powertrain department. I have 55000km on my clock and everything has been solid so far.

30000km of that has been with the JB4. But ofcourse ever since my car got flagged by Mercedes, I stopped taking unecessary risks. For example if the ambient temp is above 15C, I do not use anything more than map 1 or map 2. If I am really romping on the car, I usually just use map 0 as well.

So far to my knowledge, there has been only 1 catastrophic failure of a stock M276 engine, in a GLC450 I think. That one looked like a manufacturing defect as it happened within 12k mile. Since then I have heard of no other failures from stock cars.

We have more than 50 guys in our Jb4 group now, they also have been reporting no issues so far. Some of them have high mileage (above 50K miles) as well.

Now with full tunes however, I have heard of a few catastrophic failures due the connecting rod failing (apparently the CR is not forged but the piston is), weird design decision by Mercedes.These were stage 1 and 2 cars only and the customers apparently requested the tuner to provide a tune with ridiculous boost request. So I am not exactly surprised.

I have always felt while driving this car, that will probably get unreliable from stage 2 onwards (tune+dp). I personally do not feel like this car is meant for turbo mods without additional strengthening mods with gearbox clutch and possible reinforcement in the engine (may be it will need pistons, connecting rods and fueling system to be upgraded).

Also I know of a c43 which blew a turbo after multiple top speed runs (he had a full tune as well). He luckily got that covered under warranty.

Also I know of 2 guys who had a gearbox valve body failure. (One of them had a JB4 and one was stock). Both fixed under warranty.

That's all I know so far. May be you guys can chime in.