Mechanic says "cluster bearings in transmission are nearly shot" (4spd)

[Miles81_240d]

:-(

Well, some of you might remember that approx 3 weeks ago, i purchased a 1981 240d in great shape..i mentioned that i had heard a "rolling noise" and I got alot of good feedback, with the majority of people thinking that if anything, it would likely be something driveshaft/rear end related.. I took my car to "MBI Motors" here in Portland - they are a very-highly recommended independant MB shop. The diagnosis is, in the mechanic's opinion, is that the "cluster bearings" are going.. Now, my car makes this rolling/"bearing"-type noise when under load, be it in reverse gear or only gears 1-3. 4th does not exhibit the sound(my car is a manual, 4spd transmission, btw).. The unfortunate news is that to have the trans overhauled, which i believe would be the only way to save the transmission, per the mechanic's advise, would cost approx $800.. is this reasonable to pay, for this type of repair? I wish there was some cheaper solution!.... The car still shifts and drives *fine*, but the noise is there.. i dont know how long i shoud be able to drive the car as-is..? any ideas?? thanks so much guys,

Miles
81 240d 4spd (Silver)