Leak around Backwash valve

I have a Swimquipt backwash valve and it has been leaking from the top of the valve at the stem only when the pump is running. I opened up the valve and replaced and lubricated the o-rings, but it still leaks. Any ideas on what else I can do?

Barry, you've done what would fix the problem most of the time. The only thing I can think of, other than the o-rings failing, is that there is a hairline crack:( You might want to remove the handle and look at the top around the shaft under good light. Sorry I can't be more insightful.

Thanks for the reply.

I just took it apart again and installed some slightly larger o-rings. No change in the leak issue. I don't see any cracks anywhere. It seems to be leaking right around the shaft where it comes up through the top. I would think that would mean something is not sealed properly, but I don't know what else to check.

Any other suggestions are welcome.