Your Best advice

O.K.-you guys have saved me many times now i need your very best advice-and this is gonna be a judgement call...
I have a VERY well-maintained 1991 300 E 4matic with 215,000 miles-I recently replaced the tensioner and serpentine belt-only to have the air compressor seize up on the highway 3 weeks later-doing about $1600 worth of damage-new compressor, a couple of new pulleys and new belt....
Well now i have a 4matic problem-seems i may need a new differential-She sucked thru the last 1/2 quart of hydrolic fluid-now it COULD be a leak, but I filled the resevoir up with the $40 a quart liquid gold MB hydrolic fluid-and the 4matic light stays on...This is about a $2300 fix-the re-build diff is about $1600...I have been out looking at replacement cars-but I have looked at 3 already-all with under 100,000 miles-and they don't run as well, or seem as nice as my car (not to mention-how do i sell my car with this problem?-I was told I could get $2500 wholesale..) Am i just stupidly emotionally attached to my car???? A friend of mine (good friend) is loaning me $10,000 interest free to buy another car-but ONLY for buying another car NOT for fixing this one...what to do-what to do......