What causes excessive wear?

I have a '91 300TE 4-matic that I bought used about 1.75 years ago with 70K miles on it. I bought the car with a Starmark warranty, and it is a good thing I did. The car has been in the shop numerous times for a large number of repairs. The dealer (in Seattle) has been great about the efforts they've put into the car. The repairs include:

New transfer case
New steering gear
New front axles
New front struts
New steering damper
New front sway bar & bushings
Numerous hoses (hydraulic)
Replaced the valve guide seals
Replaced the front and back brakes (rotors & pads)
Several repairs to the vacuum systems (seats & locks)
And a list of other stuff too long to go into. Literally, I have a stack of repair related paperwork that is over 2 inches tall.

The car is nearing the end of its warranty period. I have several friends that have 300E class MBs and none have had anywhere near the amount of problems my car has. The mechanic said he put in about 100% more work than he's ever put into another 4-matic before…

The car consumes about 1 quart of oil every 3K miles. The question is, even with the monumental amount of work done on the car, and given that it is working pretty good at this point, is it reasonable to expect that it will continue to work okay without further significant repairs? Or should I cut my losses on the car and go for a (new) ML 320 instead?

Comments are welcome and appreciated!

…tracy