Hate to have you go through extra work, but it might be worth lowering the tank and taking a look-see inside to make sure that something did not come loose/off, such as the sock filter or pickup tube.
Your tank is well past the batch that got a booger weld blocking part of the outlet tube inside the tank, but that's not to say it could not have happened again.
Of course, since it sounds like it was up and running fine previously, it's probably not one of the permanent fixtures, but more likely one of the attachments. Hence my thinking about the sock filter.
Although, buying a new pump anyway is not out of the question. Having an extra pump on hand is never a bad thing.
Paul