I don't want to confuse this well taken care of thread. But...
The ZTL M/C is 14mm, and one for the later ZTL-2 is 19mm. (IIRC, but they are definitely different)
I've had sticking problems with the lever similar to what you describe and a touch of grease on the tip of the M/C piston will allow the shoe on the lever that contacts it to slip across its face and make it surprisingly smoother.