Angry transmission at low/stopped speeds

[rede30]

The tranny in my 88is DD is giving me some troubles. At times when i drive it and then come to a stop the tranny locks up and wont allow my to get it into or out of gear- this is a 5 speed. I also feel like there is a bit of sticking at times, like the car doesn't feel like it is fully in Neutral. The clutch is new- and reinspected, the slave is new and the master pumps well. I think the tranny has 427 on it and i would fully understand if it was going on me but are these symptoms of a breaking 260? I do have a small leak out the rear of it, i have not had this car too long and figure the fluid could be low, would low levels give me these problems? What size Allen gets those plugs out? Are there two sized plugs on these trannys? i feel like the 5 speed i just drained had a smaller allen size. so if there are a known two sizes, mine is bigger because i do not have anything that fits the plug.

update: the master was the problem.

[nickpdx]

My tranny has had a very slow leak at the output shaft seal since I bought it (which I am actually finally getting taken care of within the next couple of days) and it was pretty low on fluid at first and a bit "clunky" and rough. Sometimes it would be hard to get into 1st or 3rd. After draining the fluid that was left and refilling it with Redline MTL (which I top off regularly) all those problems went away and it made a huge improvement. Should be a 17mm allen socket.