Wow Chris, it sounds like you got a bad apple.
It's sad to see someone so dissatisfied in a Mercedes. I have 2 E320, both 1996 Vintage and i love them to death (except the spring perch falling off on the Green One, and the rust that always seems to creep up...) But i must say, the reliability of the car starting every morning and getting me where i need to go is exceptional. The M104 engine is by far one of the most reliable and enduring engine's in the world. The transmission on your car was probably never serviced by its prior owner. These trannies should be serviced between every 20-30,000 miles. When purchaseing a pre-owned mercedes, it is important to have the car inspected prior. All of the problems that you had to take care of on your car were pre-existing, they might have been picked up with an inspection. All the best in what you decide to do....
And as far as Lexus goes- do not even get me started. Yes, the fit and finish is nice, but the constant engine sludge that plagues them year after year never seems to get noticed? How about replacing an engine on a 2 year old RX300 and an engine in a 3 year old LS430? Yeah- you never hear about that stuff until you know someone that works at a Lexus dealership....
Just my opinion....
