TargetTalk

Can someone let me know if there is any downside to leaving a
full or near full air cylinder (Morini, Steyer, etc) for a long period
of time (4 - 8 months), aside from losing air pressure.

Thanks

Rubber seals under air pressure age more rapidly. They develop permanent deformation more quickly resulting in more frequent airgun repair. Releasing pressure is a more conservative approach.

Your mileage may vary.