While I tend to subscribe to the "if it's not broken, don't mess with it" philosophy, I serviced my own by putting the deep springs on my Aquatica housing after about 3 years of ownership. There was some grime on the o-rings behind each button and I felt better for having cleaned and changed them to less-squashed ones. I took the housing for a camera-free dive after the o-ring change to make sure all was well before submerging the camera again.
You'd want to have some spare c-clips on hand too as some of them go "ping" and disappear during removal.
If you have to mail the housing to get it serviced, I'd say the risk of it getting lost or damaged in transit is greater than the benefit of annual servicing.
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