The cylinders from quick fill and non quick fill HW100's are interchangeable.
The leak if it is not the small o ring on the little cylinder connection spigot is probably the ones around the outside of the sleeve in which the regulator piston sits. A leak here often leaks out of the small hole on the bottom of the action just like the cylinder joint seal does but continues after replacing that one.
HFT, for people with only 2 buttucks!
VooDoo TwoTwo The next chapter.