Hi Josey and a very warm welcome.

Some of today's budget guns can be good. Some very good. Some not so. However, especially taking into account the mention of sentimental value, I'm with Dave........do the Airsporter.. Do we know what age / what version it is? If it's of a certain era it'll most likely be the buffer behind the piston head unit that has degraded, turned to mush and gummed things up.

The parts diagrams from various parts suppliers, like Chambers and Knibbs, will help. And there have been lots of threads detailing the stripping of these on here. You're in the right place and are sure to get some sensible direction and advice from the BBS collective.

Enjoy.