Good suggestion. However, I took apart the Hayward Vari-flow and the spider gasket looked ok. It was a little worn, but no major flaws. I replaced it just to be sure. Is there anyway that the valve and attached openings can be off kilter? I did not see anything visibly wrong.
I am beginning to suspect that I'm losing pressure from the DE somewhere. The internal pressure is not climbing above 12 (ten is normal after I backflush and clean), and usually by now, I've needed to backflush the filter a couple of times.