I have an old Hitachi frame nailer, but the tag(s) are missing. I'm not sure what modle I have. The gun stopped working and has an air leak coming from the top exhaust area. I would like to keep and get it fixed. Any thoughts?

maybe its your connection thats leaking and not the nailer.

If your using refills that have wire holding the nails together.
Check to see if bits of wire, debris is collecting in around the striking hammer. I switched to paper and never looked back. Must have gone through 5k worth of nails and rarely jams. Other things to check,
1. Check the striking hammer, make sure it is not bent or damaged.
2. Check air pressure, Low pressure can cause jamming, misfires.
3. If the tool needs pneumatic oil, 2-3 drops before you start good rule of thumb.
4. Check spring return. Sufficient pressure must be maintained or the nails will not feed properly. Misfires, incorrect feed, jamming etc.
I had a Hitachi brad nailer and it was horrible. Fire 1 brad nail would jam or misfire. Did everything I could think of nothing worked. Put it up, got a Rigid brad nailer and never looked at the Hitachi again. :)
Sometimes you just get a lemon! (PS I understand you have a framing nail gun. Brad nail gun above is used for an example)
Hope this helps

Just as a matter if interest, were you using the tool in soft or hardwood? This is something that only happens if repeatedly used in an extremely hardwood like Ekke or similar. Did Hitachi resolve the problem with you?

Regards
Alex

use the lube that came with the kit, you can replace everything correctly but if oring gets pinched it will still leak

Place two drops of light oil into the gun at the air inlet, and re-connect the hose. Fire your gun several times into scrap wood.

Best regards, --W/D--

One or more of the rubber o-rings inside the gun are worn or broken. Air is leaking out of where it needs to go to push the driver back up. This is a good gun and worth rebuilding. Unfortunately Hitachi doesn't make rebuild kits for their guns, you have to have a breakdown and order each part you need seperately. If you do this, replace all of the o-rings, if one went bad the others are not far behind. If you take it to a repair shop make sure they repalce all the o-rings.

if you took the trigger apart the part that you unscrew has a nylon ball and a black rubber ring you should check them and make sure that you didn't loose them when you took it apart,if they are there, then you need to service the gun, and after you clean all the moving part and you put it back together, it may still leak from the top,Take a rubber hammer and give it a good hit,now not to hard, and it should seal

yes my guns i rebuild once a year at least

If the gun is blowing air out the back cap it needs an overhaul. If you take it to a service center they will be able to supply you with the proper O-Rings or if you pay a little more they will overhaul it for you.

Oil leaking out of the nailer anywhere is just an indication that too much oil is being introduced. A good solution would be to reduce the amount of drops until no more leaks out or use an in line oiler at the gun. An oiler costs under ten dollars and feeds in oil vapor as you use air. Store / hang your nailer with the air inlet down at night to drain out access oil. Do not worry too much about the leaking though, I think that a bit too much oil is better than a lack of oil. Good luck.