The most common part that needs to be replaced on a Varios pump (we highly recommend having one on hand at all times) is the impeller. They usually need to be replaced every couple of years as the polarity of the magnet wears out. I also recommend keeping a pump bushing on hand as well, sometimes carbonate build-up on the impeller shaft can cause it to seize onto the shaft rendering it unable to spin. You can purchase both parts on our website here:
https://www.coralvue.com/reef-octopus-varios-rodc-water-impeller
https://www.coralvue.com/reef-octopus-rear-pump-bushing
Please let me know if you have any other questions.