FYI; I bought the entire multi port valve for my sand filter through Amazon. I’m sure it’s not the same as yours but when I was looking at fixing the one I had vs just putting in a new valve, changing the whole valve was the way to go. It got me new sight glass, pressure gauge, gaskets, clamp ring, everything...

https://www.amazon.com/dp/B00269II66

Might be worth checking for an entire multi port valve vs parts. Just a suggestion...