Slight muffled clunk heard infrequently, 3-4 seconds after shifting
into 1st and 2nd, from what seamed to be drivers side rear.
 Recently put in reverse and went about 6 inches.  Could drive
forward but reverse would lock up at the same 6 inches.  Could go
forward but wound up against a wall.
 Jacked up drivers rear wheel rotated forward freely .  Would lock up
on 1/4 of a tire rotation in reverse.  Lowered and rolled back 6
inches ,raised and lowered then got tire to spin backward several
rotations.  Lowered rolled back 3 feet, locked up.  Jacked spun and
lowered.  Rolled back clear of wall, put in gear drove home 70 miles
without incident.  Parked and started driving my 850.
 Got back to 240, put in reverse no problem.
 Put up on stands removed rear plug and drained gear oil.  Oil looked
clear, but magnet had about 1/8 inch of metal sludge and some small
metal splinters.
 I can get a rear for $250 from a junk 91 and do a whole swap, but
it's 0 degrees here, I do not have the time, and I would have to
change all the bushings, springs, shocks, stabilizer bar if I had it
all apart, and I can not afford that now especially if I have to buy
the rear.
 I could get the rear and swap the gears but  I'm not anxious to fool
with pinions and shims and axles, and will it howl when I'm done.
 I could get the rear and see if the dealer would put it in, but that
might be the cost of all the other upgrades I would like to do. (when
it's warmer)
 Anyway, any posts anywhere of a rear gear swap, or rear end swap.
 Can I use a 740 rear, or the gears from a 740 or any other model.
 The Bentley Manual says I have to feeler gauge the speedo pickup in
the housing, but not much about a removal and  replacement of the
gears themselves, except that you should leave it to the Pro's
Thanks
Ray