I ran into this problem as well. Ended up going to a local reef supply store and he had a couple used ones. They work waaaay better.Sorry to bump this one, but I ran into the same problem. Amazon to the rescue!
https://www.amazon.com/gp/product/B06XMXLFV3/?tag=skimlinks_replacement-20
It's damn near the same pump that comes with the Mark II. Might be a hair taller, but works with all attachments and plenty powerful.
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