Thanks for the responses.
The secondary ignition system looks like it was done, but I will look at the bills tonight and see what make they were.
The O2 senser was replaced recently... I assume cos I see a bill for the part!

I agree that it sounds like an ignition issue because of the suddeness of the stall.
I am new to MB, but have a quite a lot of mechanical experience, so what tools will I need to check the duty cycle? I have a good analog multimeter, but love tools, and always prefer to buy and invest in stuff that pays back over time!
Or would it be better/cost effective to just take it to my local Indie?
It seems from a lot of the posts that this issue is difficult, expensive and hit and miss even using the Indie!

Should I order a new OVP?

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2009 Mercedes ML320 Bluetec