I'm sure I'll catch a ration of doo over this statement, but in my opinion they are junk.
I've used several in the past that came with used set ups. And had trouble with every one of them. One was the cheesy ceramic impeller shaft breaking several times, another was the exact problem you are describing, another was the cheap locking handles breaking at the canister body, and most of them you couldn't get a good seal between the motor housing, and canister base. So they would suck air and either quit completely, or have a very low flow. Not to mention they are a PITA to prime.
That's what I meant by(because its a Fluval)
I wouldn't take one if it was the last filter available!!!