Try RatRacer's suggestion to try to narrow your search.
But you touched on something: Poor quality control upon assembly. The Mrods have been known to be assembled a little on the sloppy side, with o-rings sliced on insertion. And like most any firearm, the assembly lube and assembly environment aren't clean. With demand high, some quality in assembly might diminish. I hate to say it, because I hate to do it myself, but tearing it apart and looking at everything is probably your next step. I don't mind that part, it's just the assembly to proper specs, and educated smoothing that I'm still an amateur. While a lot of people can do what a good tuner can, and I'd like to get there myself one day, I find a good deal of benefit in having a tuner 'blueprint' and 'smooth' a gun to have it working as designed, not as assembled.
That said, you probably just have a nicked o-ring that you can replace on your own, with minimal cleaning while you're in the area.
Prod (tuned by Paul B., LW barrel, RB grips, ACE Folding stock, camo, TKO & JG brakes)
Sold: .22 Mrod "The Toad" (tuned by Paul B., 18" LW barrel, Toad-A-Flage camo)
Sold: .25 TT Mrod w/ reservoir and shroud extensions