A leak from under the screws in the multiport, and from the backwash port, and from a ball valve does not sound like a spider gasket problem: it sounds like your filter piping froze with water present, and cracked a bunch of things.
Is this the valve you have?
If so, I don't quite understand your phrase "right where the nut and bolt is" -- there are 6 or 8 stainless machine screws with nuts that hold the handle plate down. Is that what you mean?
I don't know that any of this is related to your skimmer cracks, but freezing problems could definitely fit the description you gave in the first post.
Ben
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