Well
I don't know of someone has already get this mechanical problem.
I wanted to change the inside ring N°123450 because i felt it dead ( no more resistance when i introduced the needle), no more full watertight.
The problem is it was very hard to unscew the N° 123471 .Impossible to get it . I'don't know if because i've used a too mush small screwdriver but it sleep inside and i've killed the scew head .
One of notch is completly round and i Can't get it , even with a bigger screw driver, no more good grip for the screwdriver.
Sure i have squeeze the crew by turning too hard the last time i've changed it.
I've tried also to let in thinner in case of too much dry paint, put some product for jam.
If someone has an idea !
Thanks
pat