When the bottom spring of the valve is broken, the forks will lower very very slowly. The spring in question is not to be confused w/ the hand recoil spring.
Internal to the lower spool is a sliding valve (as I recall) that is spring activated. When that spring fails, the forks drop slow. Access to the spring is to get a pair of "opposite plyers" and pull out the section. Again be advised, once you remove the slide valve, it must be replaced, so be sure of your problem.
I isolated the problem before I condemed the control valve.