I just changed the pellet probe o-ring on my Daystate MVT FAC. Was not aware how important that was but suspected that something caused accuracy issues. I could not see on the old one any the small cracks, cuts, or deformities with the naked eye. Once replaced, it restored accuracy to what one should expect from a Daystate rifle. I heard others replace their pellet probe o-rings every 500-100 shots. They are cheap enough I guess, just make sure you get the right Duro number. For FAC or high-power Daystate says Duro 90 and for lower power or 12 ft/lbs a Duro 70.

As far as the others o-rings, some replace them every two-years, some never. If there isn't a leak and you have no accuracy issues, I would leave the alone. If you are already inside your rifle for some reason, you may want to replace them anyway since o-rings are not that expensive. Always use some silicone grease to make them last longer.

Not sure about other brands and types, I let others chime in.
 
 Not sure about FX & such but, good ole' crosman recommends lubing the pellet probe (inside the barrel) o-ring every 500 shots. This does seem to help them last longer.
We have an AA410 bolt action ( 10 year old?) that still has all original orings and is still prefect.
As far as internal O-rings if using the rig for competition "I" would replace all seal/orings at least every ten years.

John