I just cleaned my DE filter and after reassembling, I can't get it to pressurize. Its an old (20+ yrs) Swimquipt with the panel type filters. It seems to fill, but it never builds up pressure. Yesterday the needle would move up for a few seconds, then drop back to zero, today it just stays on zero. I've cleaned out the skimmer basket and the pump basket. I took it apart again and cleaned the rubber seal where the two halves of the filter housing go together. Is it possible that the filter is just shot? If it's worn would that keep the system from pressurizing or is there something else I could try. Any help would be most appreciated.

Thanks,
Barry