I have changed them once already, the unit is coming up on 3 years old. We get a lot of high winds here and cold winters, I suspect the bearings are designed for more temperate climates and wear quicker in the -30C/50+km winds. They both quit in the depths of winter (basically ceased bearings).
The original VP anemometer must have been designed for a wider range of climate, it is still going strong, even though something broke one of the cups off the spinner, which was not a big deal to replace.
Good to have a spare in case, the part# is 7345.953 I think for the VP2 cartridge. This is just for the anemometer, not wind direction indicator part.
Cheers,
-G.