Hi DaveinMass,
Normally the issue is a bad spider gasket. The SP711 valve’s spider gasket is glued into the diverter and can only be purchased as such. Did you replace the diverter with the glued in gasket or did you purchase a spider gasket by itself? My concern if you purchased the spider gasket by itself is that it may have been a spider gasket for a different valve that does not have the exact same dimensions (slightly off). If this was the case then I would purchase the Diverter with Spider Gasket Glued In and do that replacement. Below you can see how the diverter with gasket glued in looks.
Another option is this Complete Top Handle Assembly W/ Spider Gasket Glued In I have also shown a picture of this item below.
Thank You
Patrick