Greetings Learned Friends

Having moved over to the US from the UK a couple of years ago I've finally got over the mid-life crisis (I bought a Mustang. I know... the shame) and want to get back into MB ownership having owned a few in the UK.

I want AWD. It so happens there's a used car dealer down the road from me that has a silver with black leather 2004 ML350 Inspiration with ~38k miles on it. They want $15,995 for it, and I'm think of going in there with an offer of $13k as it's been around for a while.

I've a few questions, which I'm hoping folks here may be able to help me with. The car's sold "as is", although an extra warranty to 100k miles is available. My experience in the past leaves me with mixed feelings on that, is the collective opinion that that would be worth getting?

I've read the postings on things to look for, and intend to take a fine toothed comb to it, inside and out, and take it for a lengthy test drive. I'm keen to understand what sort of servicing costs I should be looking at in the future, and if I should look out for a quality third party mechanic, which is my inclination from a value for money perspective. I'm in the Pacific Northwest, near Seattle, so any recommendations on 3rd partys in that area would also be gratefully received.

Any ownership advice is gratefully received, along with recommendations on obvious things to looks for.

Many thanks folks!