The only thing I have noticed breaking down like that is the rubber flap in my commode after using bleach tabs. What type of cleaners have you used on it?
Have you thought of a polymer 80 pistol build when you get to NM? You would need to source everything beforehand and have it waiting. Then finish the lower and assemble. You would not be able to take it back with you and cannot sell the lower. You should be able to sell the remaining parts though.