Thanks for the post!

There are a couple of reasons for this happening.

1. The Cylinder Seal or other o-rings are damaged on the Cylinder inside the nailer.

2. The Trigger Valve has damaged o-rings.

3. The Head Valve has damaged o-rings.

4. There is a lot of grit and/or debris inside the nailer body (cylinder, head valve & trigger valve).

I would take the Head off and remove the Head Valve, Piston/Driver assy and Cylinder and inspect for debris and missing or damaged o-rings and seals.

Most likely replacing any of these seals and simply cleaning the gun (and oiling it afterwards) fixes any leaks you'll find when operating it.

You can find a breakdown of this nailer by clicking on the below link:

www.mastertoolrepair.com/pneumatic-frami...s-f21pl-p-12215.html

Let us know what you find after taking it apart!

- MTR

Good to hear you pinpointed the problem o-ring.

This is pretty typical, and many factors can cause this. High humidity is one of them. Just make sure you keep the nailer clean and always pour a few drops of pneumatic lubricant in every time you use it; also add lubricant when you store it for any period of time.

The head valve is a moving part, of course, and these o-rings see a lot of wear. As long as there is no grit/debris inside the head and the o-rings are properly lubricated you should be fine.

- MTR