I run about 10 vulcans for our church's nerf ministry and have done the exact same mods u have(plus new marabuchi motors, reinforced plunger rods and 25v lion packs). Recently two have stopped working. Upon close inspection there were what appeared to be discoloration on the plunger tubes. They were actually cracks that formed but really didn't open until the gun was in use. I fused one crack back together and it works again. Hope this helps!
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