I have a early MTH PRR RS1 that is showing gassing on the underside fuel tank...I own three of these (all the same all PRR) and this is the only one doing it.
What I find amazing is I own a fair amount of MTH Die-cast freight cars...boxcars reefers hoppers gondolas and cabooses (63 in all) and I have inspected all of them and found no evidence of problems....yet !