I think that any cylinder with hydraulic pressure pushing the rod out of the bore will leak if the hydraulic pressure isn't governed. I would pressure test the hydraulic pressure supplying the p/s cyl while the cyl is cycling in & out (not dead heading either direction) vs deadheading the cyl in both directions. I guess is the hydraulic pressure is spiking & overcoming the seals.

I'm curious to hear your results after you adjust the throw of the cyl by adjusting the stops. Keep us posted