I GOT IT!
Why I didn't think of this before is beyond me... DOAH!
So, the original spider gasket really was bad. My general feeling was that the problem got worse (a bit) after I replaced the gasket. Since things bug me 'til no end until I figure them out, I've kept learning & thinking. Finally I just pulled the diverter back off. I wiped off the lube from the gasket (but relubed the o-ring) since no one ever heard of that before (thank you forum & no thanks pool store). I also felt around, since it *looked* fine, the area where the spider gasket makes contact inside the valve. It didn't feel perfectly smooth. This is the key - I took some superfine 0000 steel wool & carefully cleaned the area inside the valve where the spider gasket makes contact to ensure there was no gunk there & it was smooth.
No longer am I getting leaking to Waste when filtering.
"Party on Wayne..."