I believe that this is what you are looking for....
I sent a Mossberg Plinkster with a magazine issue and cartridge feed problem to Gretch. They test fired it and sent it back unfixed -said it worked fine. Not impressed. I am out the shipping and still have broken Plinkster.
Do what I ended up doing, go over their heads and deal directly with Mossberg.
Also Wortners is a Mossberg warranty center. Ask for Peter.