I had the exact same problem, though mine never bothered me when darts were fired, mine broke as a direct result of my little brother dry-firing the gun.
I fixed mine though a needlessly involved process of pinning the plungercap back on to the tube, Took a dremel, grabbed a 0.5mm Drill bit, and carefully drilled 4 holes around the edge of the cap going down into the wall of the plunger tube at a slight angle, so when the pins were put in, they were less resistant to pulling back out
Then gooped the whole inside edge and outside with play hobby Superglue, the kind that nearly dissolves some plastics, and squeezed the cap and tube together again. While it was drying I took some very small pieces of wire, 0.5mm, actually, and gently tapped the pieces down into the holes, and bent the ends over the outside of the hole.
This way, the holes and the rim were completely glued together (nearly fused thanks to the glue), and I've now managed to get another 4 months and counting out of the same tube.
It requires a little bit of precision, but not alot. Just patience =)
Recons cost a small mint in Australia, so I try not to replace parts or buy new items if it can be avoided.... It's really only $50 AUS, but thats more than Im willing to throw out of pocket each time something bungs up =)
Try my method, if you need a visual explanation at all, just ask =)
And sorry for not helping your deal Diamond =) Hehe
Edited by Ethendel, 06 April 2009 - 08:19 AM.