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The CA350 uses 2 608 cartridge bearings in each fan. I don’t know if the CA550 uses the same fan assemblies, but you can probably determine this by comparing part numbers in the Zehnder manuals.
I have two CA350s in my home and have had to replace bearings in 3 of the 4 fans over the past 6 years. Replacement is easy if you have a bearing puller (~$20 for a tool that clips onto the inside bearing race, filling the center so you can use the fan’s own axel or a circular rod to push the bearing out). I decided to switch to sealed cartridge bearings from Phil Wood. These bearings likely have slightly higher drag than the originals, but should have significantly longer lifetime because the seals keep out dirt/moisture and help to retain the lubricant.
For an assembly that doesn't really see much dirt/dust, if you're concerned about drag you can use shielded bearings instead of sealed bearings, as the shields don't physically contact the bearing races and don't contribute to contact drag. Honestly though, seal drag isn't anything to worry about in most cases.
Many industrial bearings will come pre-lubed with Mobil Polyrex EM (Electric Motor), which is a perfect choice for a long life application like this. I've used it for years in things that don't have anything to do with houses.
It sounds from this thread that the bearings are a different size in the CA550:
https://www.greenbuildingadvisor.com/question/replacing-bearing-in-zehnder-fan
The original bearings in my units were shielded, but quickly lost lubrication and showed signs of surface rust - the first failed at around the 2y mark, the next about 6 months later. I have an ERV core, so I expect that means the bearings on the extraction side see pretty high humidity which contributed to the premature failures. It took almost 6 years for the first intake fan to start making noise, so the conditions seem very different between the two fan positions. Both fans are identical.