CGT won't stay in reverse

[Craig D. Niederst]

Our '86 CGT has had a problem with reverse ever since we purchased it, and
has gotten progressively worse as of late. When you shift into reverse, and
let out the clutch, the car pops out of gear. Sometimes it happens
immediately, other times after a couple seconds. Feathering out the clutch
helps somewhat, but it still pops out. Trying to hold the gearshift in place
also does not help. It seems worse when I try to back the car up our
driveway, which has a decent grade. When it slips out of gear, there is
usually a loud banging type sound until you push in the clutch (which I
always do very quickly!). This problem does not occur for any of the forward
gears, and the tranny generally shifts very smoothly. I find it hard to
believe the actual reverse gear has gone bad, considering it should be the
least used gear in the whole tranny. Any ideas on what could be going on
here? TIA.

Craig
'92 100S (90k)
'86 CGT (194k)