I have located a 99 ml320 with 130k miles for $2500. It is a
Salvage title car that has been rebuilt. I. currently own a 82
240d and know what to look for when buying a 123 series.
What should I watch out for in the ml or for a guy with little
disposable income would it be better to walk away?

I take it from the lack of responses that my question was missing information.
My son is looking for a summer internship the 240d is his to drive when he is home.
If he gets an internship in a large city I don't like the idea of him taking it because it
Doesn't have much power plus if it needs anything done to it don't know that he could fix
It. So I'm looking on craigslist for s..ts and grins and find said ml. I don't know anything
About them or weather it's a good price

I would almost want to recommend walking away, given the "little disposable income", unless it goes down hard and the possiblity of starting over with something else (in other words being prepared for a repair estimate big enough to choke a horse and just cashing in your chips for whatever someone will offer you for it and buy him another vehicle somehow appeals to you). Maybe $2500 is the price for what seems to be a "beater car" these days. A beater car to me is one you buy and don't really stick much money in to, just normal maintenance and if it goes down hard you simply replace it.

The transmission seems to be everyones big worry with the 97-98 on up cars with the 722.6.
At this "price point" I don't know if you'd have any records on it.
On a salvage title MB won't even recogize the vehicle as a MB any more, so probably no way to find out anything about it from them.
But if there is any paperwork showing maintenance has been kept up, that would be good.
Fuel pumps were a sore spot on these, not sure if that's the case at this point.
Can't really think of too much else, drive it and see what you think of it, check the tires, brakes, find out if the sparkplugs have even been replaced, see if the trans is leaking, how does it shift, is it burning oil (supposed to be running on gas in case you forgot, dieselboy, LOL). Just give it a good once over or pay to have an inspection done, $100 to have it checked is not a bad investment, but I'd want someone who works on Euro cars to do it, not the tire store down the road.
What does your son feel about an SUV over a small economical car? I would think a small car would be better suited for a large city, maybe he'd even want a scooter, but I don't know where he is going or much else, so hard for me to say.
Are you talking next summer because summer is over, kind of late to take a summer internship..
EDIT I'd also find out what the salvage branding was about, flood damage or is it two different trucks taped together or what??? If it was something like flood damaged and was from a long time ago, then 2500 might be a good deal, just an unfortunate thing that happened but an SUV would probably be better to survive this in "normal" condition than a car, but if it is a Frankencar, then it probably is only worth the last 3 digits of that price.

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Passed on the car. The guy selling it was 2nd owner 1st had hit a deer
in it. That's why it had a salvage title. Looked good & ran good but to much
Could go wrong. Yes next summer is when he is looking for an internship.
Hopefully in St. Louis (close to home), or Nashville. The type of car doesn't
Seem matter much as long as it gets him from point A to B. Of course being
Young a sports car would be prefered haha.

and the ml doesn't get the best mileage, understand about 123 and 124's loved them, and had a mom by her daughter my 300d turbo wanted the kid in a safe car