Do you have the tailhousing off? Remove any tension on the band and the pin goes out of the case to the rear, be sure to replace the o-ring in the case for the pin. It can leak and make it look like the pan gasket.
IIRC, you have to remove the tailshaft housing to get that shaft out. It's been a long time since I had one apart, so don't take my word as gospel on this.
You should be able to loosen the adjustment, if still not enough pull the small strut (1"x1"x1/8" steel piece) out and it will rotate around far enough to get the piston out, r&r the spring and replace piston.