Could I get some opinions/info on a comparison between the '87 300D and earlier '80's 123 models? Different characteristics,aside from body style? Handling,durability, and maintenance etc.? Is the '87 considered an "improvement" in any way,or is it just newer? Thanks for any replies!

Check this out

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2412482893&category=6330

That looks like a very nice W124 300D Turbo w/ the OM603 motor.

I have never owned this particular W124. However I've test driven some 1994 + W124's namely E500s and E320s.

I don't know how the 1987 model drives. However the W123 is definitely old in comparison to the W124. Just about everything in the W124 is better in my opinion.
Except maybe if you really like the way the 123 looks.. I do

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2008 BMW 335i Coupe

When things start to break, it becomes very expensive on a W124 chassis, as opposed to the W123 chassis.

Things are much more advanced on the W124 chassis, therefore much more non DIY friendly, and therefore more expensive to fix (both in time and energy) for those reasons.