Thanks for the post!

The bumpers would not cause this leak when the tool is at rest, only when the tool is cycled and the driver piston is seated against the bumpers, so I'd rule these parts out.

It is also not the nose.

Any leak from the nose comes from the outer diameter o-rings on the cylinder sleeve or cylinder ring/bulkhead ring.

In a tool of this age, it can even be the hard parts if there is scoring from years of use and grit in the tool.
All of the listed parts seal together to create a seal between the upper chamber and lower chamber and if any of them leak, it comes out of the nose. At rest, the tool only has pressure in the upper part of the tool.

o-ring - OD cylinder sleeve
o-ring - OD on the cylinder ring (White Plastic Collar)
The cylinder ring itself
The cylinder sleeve
The frame

Obviously the last two are least likely, but very possible.

If these o-rings have been changed, the next most likely is the cylinder ring (all of these rings are in the kits) The plastic collar is designed to wear rather than wear the hard parts such as the frame and cylinder sleeve, usually due to vibration and abrasive materials such as sand floating around inside the tool. I call it static o-ring wear.

Attached is a picture I put together for something else, but all of the parts seen in the cross section can cause this!

- MTR

That's the only cross-section pic I can find, I'm afraid.

There are o-rings towards the bottom of the Cylinder (at the nose end). Any of these o-rings could cause the problem you're experiencing.

I doubt the Head Valve o-rings in the Head of the gun will cause a nose leak, that's very unlikely. If these o-rings were defective you would get a constant leak from the Exhaust port on the Head.

You can see a full breakdown of this gun by clicking on the below link:

www.mastertoolrepair.com/pneumatic-frami...-n95rhn-p-15702.html

- MTR

I don't have any more of the cross-section pics, but I'm sure if you contacted Stanley-Bostitch at 1-800-556-6696 as they can obtain more for you.

I actually had my Bostitch rep dig that photo out of his files; he didn't have any others similar.

- MTR