id be up their azz bad. if the product you purchased did not perform in the advertised and represented manner, they are at fault. did your modification alter the structural integrity of the part?
if not, the defect is not your liability. time seldom agrees with restorers, and builders. parts sit for untold time while other facets come into fruition . i have never encountered resistance due to that factor thank goodness. all the vendors i deal with know full and well how the real world works.
no crying, just fact, they sold you junk. and the warranty gimmick sounds like an excuse, and excuses are for folks that cant answer with fact.
if your pal cant help you, i will.
just keep it in mind, and i hope things work out for you.