It should be done every two years as they tend to collect water over time but if you're on lease and don't plan on keeping then 3 years shouldn't be an issue.
However, it is safer and if it lets you sleep better at night and put your mind at ease, I'd say go for it.
This is an extreme maintenance schedule if you plan to keep for as long as possible.
https://www.bavauto.com/media/import...ages/f32mc.pdf