Recommendation is no more than 10% squish on o-rings for dynamic movement. perhaps the inside finish of the cylinder is a little wavy, and too low tolerance to enable 10% squish? If so you may need to look for a better piece of tube, or consider cup seals like Engel tanks. They are very large tanks you have built there.
In my line of work, we use a lot of pneumatic motors. These were traditionally constructed from cast iron, with nitrile rubber cup seals, and lubricated periodically with a mineral based oil. Despite frequent maintenance, they were often a source of problems, especially as they aged. A few years ago, the motors were re-engineered, with mainly aluminium construction, and Teflon (PTFE) coated cylinders. These have proved to be exceedingly reliable and need zero maintenance over their lifetime (which is considerable). I've seen companies that offer the coating surface, but I don't think they deal with the small quantities modellers want. Shame as it would make an ideal tube for piston tanks, with the teflon coating being self lubricating, waterproof and hard wearing, and the aluminium tube providing a nice concentric bore for the seal.