X valve full auto

So I have run into a problem I just can't figure out. I know there are a lot of smart minds that browse this forum and I am hoping they might be able to help.

I have a x valve with level 10 bolt (zero shims & 1.5 carrier), stock on/off assembly with 0.750 pin, and gold spring. When I pull the trigger it has sustained auto response and then stops when I release. This valve came from a tac1. I spent my saturday trying to narrow down the problem by switching parts with another identical tac1 set up that shoots without problems. I started by verified all o rings in the level 10 bolt and on/off assembly were ok and lubed. The velocity was adjusted during the full auto bursts with trigger pulled and didn't seem to change its behavior. I then changed the on/off pin with a new 0.750 without success in eliminating full auto. I started swapping parts with the tac1 that runs flawlessly. Swaped trigger frame with rail and sear, didn't fix. Then I moved onto swapping on/off assemblies and didn't fix the problem. I then put the good valve with the bad valve rail, body and frame and found it shoots with no problems. This is how I started zeroing in on the valve. I was a little shocked that the good valve's on/off assembled in the full auto valve didn't fix the problem. This is where I am not sure where I go from here. It's not the sear or on/off assembly which are what I thought are the two most common culprits to the problem.

Any help would be greatly appreciated!

Did the bad valve in the good marker go full auto?

Regardless, change the 006 oring on the aft side of the brass reg seat holder.

If that doesn't work, change the reg seat, leaving in place the previously replaced oring.

If that doesn't work, change the two 006 orings on the forward end of the reg pin assembly, leaving in place the two previously replaced orings.

If one of the latter fixes the issue, you can systematically put in the old orings to see which it was, keeping in mind more than one could have been bad.