Inherited S&W mod 1000 20 gauge

pistons melt quite often on this gun, as you learned. s&w sold the entire shotgun lineup in the late 80's to mossberg. both names are the same guns.
the 1000s and 1000t were the fancy grades.
i owned every one of the models. except for the gas piston thing on all of them, i enjoyed them and they shot well.

How long or how many rounds before I need to replace the (neoprene) piston buffer?

Is there a substitute for the neoprene buffer or should I order several more?....

order more. clean the gun after every use and one should last a few years.

The new neoprene piston buffer I put in the bottom of the gas tube was a tight fit, but it won't stay flat on the bottom........Will this be a problem or is there something I should do before firing the shotgun?..............I would hate it being chewed up or damaging the mechanism.

can you see whats keeping it from being flat?

The neoprene buffer is donut shaped and a little larger than the gas tube (just enough to make it snug).....It springs up on one side after it is inserted to the bottom of the tube.......The gas tube and all associated parts were thouroughly cleaned and re assembled dry.

There is nothing to keep the buffer from being flat.