There are very very few Diesel sedan options. The Jetta is first that comes to mind but I want something bigger and nicer, which leads me to the reasonably priced 2006-2008 E320. I can consistently find them for $10k. Is there a reason for that, anything I should know? Are these reliable to any degree or are there major defects?
I'm pretty mechanically inclined and can do alot of basics myself but if we're talking electrical, trans, or internal motor problems it's going to a shot and that's where MB gets expensive. A 2008 with 107k for $10.8k sounds too good to be true.

 

That makes me sad as I paid much more than that a little over year ago for an 08 with 85k... Since then I have had to do the oil cooler seals (common issue that if it hasn't been done yet will need to be done) costs about $1300 at dealer or 12-24 hours of hell in your garage... I did it myself and would pay for it next time unless I had nothing better to do.
Second issue mine had but is rare it needed the timing chain/tensioner replaced due to start up noise caused by stretched chain. That cost me around $2200 at the dealer.

I would buy an 08-09 bluetec as you get the last of the w211 chassis so very reliable and no SBC brakes.
Just keep up with maintenance and it will go for a very long time. An oil change costs about $100 as the MB approved Diesel oil is around 7.99 a quart usually but I did just pick some up for under $5. The transmission needs to be service every 39k and requires you to pump fluid into it... I use a $10 weed sprayer lol

 

Is there something that bad with have oil cooler leak other than a drip in the driveway? Does it leak on other parts and screw them up? If not i'd just let it drip, haha. I know for the oil the computer will tell you when it needs to be done, does the same go for the transmission? I hear there is some reverse sensor that leaks and will oil soak a harness and some computer module down there causing it to need to be replaced. Other than leak issues it sounds like a pretty solid car. What's the deal with the SBC brakes? Also I remember trying to do the brakes on my dads 01' ML320 and they required all sorts of star based tools and was a total *****, same story on this car?

 

Well the oil cooler leak will start off not so bad but will eventually start pupping out significant amounts of oil as it is pressurized and could potentially cause you to mix the oil and coolant (unlikely but either way has to be dealt with).
Some have had issues with seizing which might have something to do with the loss of oil pressure no one really knows as it is rare and no one has put the money into finding out why. Could just be normal lack of maintenance and letting the oil level drop.

The car won't come out and tell you about the transmission service and if you don't have records from a reputable shop on a newly purchased car I would do it immediately.
I have never heard of reverse sensor leaking on the 722.6 or the 722.9 transmissions. The 722.6 (5 speed) is known for a minor leak in its electrical connector to the TCU that if not dealt with in a timely manor could kill the tcu. That is a cheap under $20 fix. The early 722.9 have some of there own issues that is why I recommend the newest you can find 08 or just an 09.
The SBC brakes are fine and IMO people complain way to much they are great until they reach there predetermined end of life and you have to replace the $1000 part. If that bothers you don't buy one with it same goes for the cars with airmatic if the cost of replacing the shocks bothers you don't buy one.

Don't know why you would need the Star system to do brakes on an 01 ML320 I don't believe they have anything complicated in them. But maybe I am mistaken either way any modern Mercedes would be much cheaper to maintain if you had a star system. Sadly every new car for the most part needs that companies own computer to properly diagnose it. One of the best purchases I have made was my star system has saved me 2-3k and I saved one member on here over $5,000 when they wanted to replace his transmission and 10 minutes with star resetting things it has been good for well over a year now...