If this is that 6 way drum valve there is a spider gasket in there you
can replace. Any pool store has them hanging on the rack with the
other stuff that goes bad a lot. The pool guy can tell you how to get
it out on your particular valve.

Had this same problem 2-3 times over the last 30+ years my pool has
been in use.......
Honestly replacing the gasket is not at all hard nor complicated...
and not expensive...

Bob G.