When I found the press, the cylinder was frozen in place, just before/after the home position. The cylinder wouldn’t travel down the racks, and wouldn’t return home. Today, I freed up the cylinder by focusing on the racks, the trip gear, the trip rack, and the trip rollers. Because the trip gear and trip rack were frozen, the trip rack couldn’t raise or lower, so the carriage could neither return home nor travel down the press.
Since I didn’t know if there were additional binding points, I saturated all ports on the carriage with penetrating oil. While this was soaking in, I took off the plate that protects the hardware, to access the trip rack, rollers, and gears, and learned (too late) that when the top trip roller is removed, the trip rack (the thing that looks like a saw pointing upward) can drop freely to the floor.
I cleaned the trip rack, rollers, and gear, backed off the pressure between the collar and the rollers, and removed decades of grime from the trip rack and gear. The roller and the roller pin on the gripper trip lever were also frozen (instead of rolling, the roller merely burnished its path down the press). Then, it took a few pushes and pulls to further lubricate the trip rollers and their cores.
When all was said and done, the gunk was on the drop cloth (and my shoes), all racks, rollers, and gears spun as they should, and the press was able to turn over a complete print-stroke, tripping on the return. All it took was a full can of penetrating oil.