Just in case: In these situations I remove all I can to leave cylinder and end block. Cylinder is clamped in a large (c. 8" width) woodworking vice using thick rubber sheet as a grip and with the end block clear to take a round bar, positioned so as to allow a good thwack with a mallet. Thwack usually does it but at times I have had to upend the block in a jar full of releasing fluid for a day or two.
The last one I did released with a very loud 'bang'.
Good luck ...
Cheers, Phil