Story & Clark (1926 "style M" pneumatics - except it is not the same as in the "technical book" (this is a wobble valve style). Rebuilt in maybe the 80s?

Trying to adjust the outer valve face travel gap to reduce leakage. Is there a certain amount of leakage expected in these valves? Seems adjustments may reduce but not completely remove leakage on this instrument. If some leakage is expected how much? Testing showed some valves leaking about 1" of vacuum pressure.

Thanks for any help.

Parks and Sons Piano Service