Bostich Finish nailer hanging up
I've only used a few pneumatics in my time &amp; one that was doing the same thing, turned out to need a re-build. Here's one place to find parts or maybe a re-build kit. The owner of the tool tried lubrication, but it didn't do anything. I was told at the time, by another carpenter, that any abnormal behavior is the beginning signs of gasket wear.

So, I got a re-build kit from a non-local heck of a haul Bostitch dealer/distributor. Due to, my local Vac &amp; Sew place only doing staplers &amp; the Electronics &amp; Power Equipment Repair places not doing pneumatics at all. A new spring here &amp; a new seal, there, there, there &amp; there. And, the problem was gone forever, as far as I knew, &amp; the tool owner was pleased as punch.