$6000 is fair if it's in good condition including a functioning transmission. Are you able to test it thoroughly with the bad transmission? Can you get it to a tech you trust for a pre-purchase inspection?

I'm one of the few in the world who'd pay $3000 for such a car because I don't mind swapping a transmission or even an engine and I'm of the mindset that the engine has a 50-50 chance at best of being sound.

You might pay $3000 for the car, another $3000 for a transmission and have car that will last a good long time, but there's a good chance you'll be part of the other statistic.

Before you take the plunge, check what your insurance will pay if the car is stolen or totalled. It'll be a long hard battle to get anything close to $6000. Insurance use goofy value models that are nothing like NADA and KBB. I had a difficult time convincing my insurance that a 93 300SD is worth more than a 93 300SE.

Sixto
87 300D