There are ways to pressurize a valve outside of a marker with some standard hardware to check this, if it comes to that. Just be careful, wear proper personal protection equipment, and always have a quick way to shut off the air supply.
PM me if you need more details.
Was thinking about that just last night. PM inc.
Question when I pulled out the reg valve pin assy and looked in there (This is without all the power tube parts inside) I can see something right in the middle of that small hole, is this suppose to be there?
You're probably seeing the on/off assembly. Take it out to see if that was it.
As for airing up outside the marker, if you're uncomfortable with any of this, send it to Tuna to get it fixed. Wear proper PPE, wrap the valve in a towel multiple times in case pieces go flying, and take every precaution possible.
I use the small end of a tank pin valve as an RT on/off plug. If you don't have one to cut up, you'll have to dremel or cut the hose clamp to allow the on/off pin to stick out of the valve, so air can get to the dump chamber. Cut as little as possible from the hose clamp.
Use masking tape to protect valve from scratches from the hose clamp.
That's a 10-32 countersink head bolt. Washer and nut to suit. Use a 010 oring. Only use the bolt to hold the oring in place. If you tighten too much, it throws it off center, and it won't seal. If it's off center, it also may not thread into the powertube. Don't force it. If it's correct, it will thread in just like normal.
The third pic has the RT pin sticking out. That's not the tank pin valve I mentioned earlier. If you use the tank pin valve method, it is totally contained within the on/off.
The pics should be self explanatory from here on out.
This will only tell you if it's the powertube leaking. If it does leak, and you can't tell between the powertube or the tip, spray soapy water on it, and see where the bubbles are coming from.
Remember, go slow and be careful. You might want to turn your tank output pressure down as well as your velocity, so you're dealing with as little pressure as possible.