New Guy here. I have recently become the caretaker (owner) of a nice '63 109. In backing it out of the garage the other day, it stuck in reverse even with the clutch depressed. After cutting the engine, it shifted to neutral with no issue. I restarted the truck and pulled back into the garage in first...and again it stuck and I had to step on the brake and cut the engine. Any suggestions? I think the first step is to bleed the slave cylinder to be sure there is no air. When I crawl underneath, I see it is tricky to get a wrench onto the bleed screw (it has a Series III transmission). Any tricks on how to get the wrench onto the nut with enough room to move it...and what size is this thing?

Thoughts? (Thanks in advance)