580C hydraulic gland removal

[jw3]

I am rebuilding one of the boom cylinders on my machine. The piston at the end of the polished rod was a s.o.b. To break loose, but I got it loose. My question is the gland is really tight on the polished rod, I assume that the seals are swollen tightly around it. After working the gland back and forth for 45 min, I only got it to move about 8 inches. I am tempted to hit it with a hammer but I am afraid I will damage it. I am letting it soak in an oilbath tonight and I am going after it again in the morning. Any advise that might make removal easier would be greatly appreciated. Thanks for reading.