Anyone know where to purchase a magazine tube assembly? Mossberg store seems to list every part under the sun except a 930 magazine tube. My 930 has had many years of hard life and the magazine tube is pitted, corroded, scored and scratched to hell and I'm now getting lots of malfunctions I suspect are due to friction of the piston against the rough tube and poor gas piston sealing due to all the gouges and missing tube material. The gun is long out of warranty. Is the tube stainless? I suspect it's not due to the fact it wants to rust if I even look at it sideways.