Most problems occur once early in the vehicle's life and then never occur again. The ongoing issues (brake switch, MAF sensor, EGR tube, etc.) are simple and cheap fixes and don't occur that often.

At 100k miles you are looking at all of the items that go wrong with _ALL_ vehicles with this age and use. Budget $4k for front end work, anything that has rubber in it and accessories and you'll be set for another 100k miles.

They are actually quite dependable vehicles as long as the owner kept up with the regular repairs. Most of the issues you read about had very simple and quick fixes then never occured again as I mentioned above. The bad reputation came from the dealers through either incompetance or greed using a minor repair issue (such as the $25 brake switch) as an excuse to replace $2k worth of electronics. Then the owners stopped doing the required maintenance and the vehicles started deteriorating. If maintained correctly there have been no reports I have read of major problems other than rebuilding a transmission in the 170k - 200k mile range. Something which is fairly normal for most vehicles, though it should be noted that not changing the fluid can substantially shorten the lifespan of the transmission. The vehicles were advertised as the transmission being "sealed for life", with the issue of "life" being just slightly longer than the warranty period. MB Germany has now reversed itself on this position as has many of the US dealers if you ask them quietly. But apparently MBUSA is scared of another class action lawsuit and the official response is that they are "sealed for life" and the fluid should not be changed. If they were now to admit that this advice was wrong it would open them up for some expensive claims.

As long as you have a complete maintenance history, get the vehicle checked out, and have money set aside for the normal repairs you should be fine purchasing this vehicle.