Differential 84 300D

[Palangi]

My car has a clunk in the driveline, especially when coming to a stop, most noticeable during cold weather. Dealer diagnosis is worn differential, probably spider gear, which is what I had suspected anyway. Dealer's price for installing a factory rebuilt differential is about $1800. The 123 Chassis Manual shows rebuilding the differential and adjusting backlash with compensating washers. Obviously a big job with considerable skilled labor involved. Dealer does not want to rebuild it in-house because the final cost will come out about the same only without the warranty of a factory rebuilt unit. A used unit in unknown condition from Adsit is about $750 delivered, with no real way for a shade tree mechanic (me) to install it, so that does not seem like a good way to go. I would like to have some advice from the voice(s) of experience on how to proceed with this. The car is in good condition otherwise. Perfect engine, good transmission, good interior, good body with no rust, only other thing it really needs is some front end work which I have been putting off. All that being said, in real life, the cost of this work if done by the dealer will equal about 60% of the value of the car.