[s-cars] Mercedes question (NAC)

[Erik Addy]

I know there are at least one or two closet merc guys on the list, so I thought I'd ask...
 
I'm considering purchasing a 1998 E320 4Matic wagon with 135k on it for my wife (That makes it a W210, right).
Listed locally for $7000.
Reason being: I can't stand the 2.8 V6 in the A6 Avants, and the 3.0's are still a bit more than I want to spend and everything I hear says they are a nightmare to work on (t-belts, O2 sensors, sludge, etc).
 
How does one of these cars compare in terms of cost of ownership to an Audi?  Assuming that all easy-medium difficult work done by owner (spark plugs, shocks, brakes, etc will be done by me). 
 
Do they have more/less/the same number of annoying small problems (HVAC/electrics/etc).
 
What are the big problems?  How does the AWD system work and is it prone to any problems?
 
Best web list/forums for DIY types?
 
Thanks,
Erik