My seats needed extensive pool noodle repair. I screwed them into the coil springs in the corners, and made 2 noodle arcs within the seat frame. I covered them with cotton cloth before installing so the metal frame bits don't dig into the plastic too bad. Seats are still firm after 2 years.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma