Now you're makin' progress!

The most likely culprit IS the spider gasket. The handle that's labeled "waste", "backwash", "filter", etc. is the multiport valve and the spider gasket is located down inside that.

It is quite possible to locate the instructions for changing that out online. If you can find them, determine if it's a task you want to take on or have someone else do it.

I know you have some algae/chlorine/water issues to deal with as well but I would suggest you fix the valve first (pretty soon) and then post back up and we'll all help you get your pool back to sparkling clear.