You can replace the important one.

Take out the circlip. Slide the spring assemble out. It will have 2 plates, one on either side. Then you slide out the black carbon seal. They are more fragile than they look. Don’t be surprised if it breaks, that happens. Inside of that, you will find an o ring. Change that while you have the powerhead off. The larger o ring sits around the lower bearing, and you cannot get to that without opening up the powerhead.

By the way, pay attention to the order you take things apart. Especially the carbon seal. It goes in one direction only.