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Your only option is if the company that installed the liner is willing to honor warranty by replacing tub. But most of these company's are long gone. with that said your best option is to rip entire tub out and replace it with brand new unit. I had to tell my motheri n law the same thing so don't feel bad your not the only person that got stuck with this cramp
the water gets in where drain connection meets both tub surfaces at drain, and has no way out and is growing mold and vermin