I have a Jandy DE filter with a pretty basic backwash valve (push / pull type)

I noticed last Fall that when the pump shuts off (after a cycle) that I can hear lots and lots of water leaving the filter and running into the pool. I have a sight-glass in the return line that I can see the water running through.

When the pump comes on there is a lot of air in the filter that needs to be bled off.

About this same time I started to notice water running out the backwash line when the pump is running.

I'm concluding the two are related, since I don't see any leaks anywhere else, there must be a leak in the backwash valve letting air into the system and partially draining the filter when the pump shuts off.

I've removed the valve, cleaned and lubricated the o-rings, but the problem persists. In fact it's getting worse. When the pump is running there is a lot of water running out the backwash line.

The o-rings look good, but I think that is my next thing to try and replace.

Does this sound like a reasonable thing to do, or am I way off base here?