81 240D finding a Manual Transmission Replacement ??

Not really a do-it-myself'er, but figured I'd check in for some help/advice.

My engine has 149,000 miles and I've owned it for the past 40,000.

This morning, I was backing out of my parking spot and was having trouble shifting into reverse. Put it in 1st and it then shifted smoothly into reverse. Didn't experience and problems driving 10 miles to work.

Backed out to go home and heard a loud banging noise (it was loud and ugly!!!) as I disengaged the clutch. Let it roll back so I could pull out in 1st. A few miles into my trip... in light-to-light traffic... it started making the noise in 1st, then 2nd, then 3rd. It almost sounded like the drive train and the gearbox was shifting smoothly.

Called my mechanic and went right there. He checked the transmission fluid, which he regularly checks, and it was fine. He has a friend that's a retired M-B dealership mechanic. He came over and they both agree that the sound is definitely coming from the transmission itself. Since it was up on the lift, the banging was much less pronounced.

Since there's no other way to look at it further, they're saying the transmission needs to be dropped.

Just wondering what my best options are? Is it realistic to rebuild my transmission? Is it hard to find a good used one? How much damage am I looking at moneywise?

I've recently moved to Miami so, if anyone knows somewhere to go it, would be much appreciated.

Thanks.

-------

Kent, I would buy your transmission manual but, considering my situation, am I too late? If you think it would be useful, I don't mind paying to discuss my options with you.