O Rings can last a long time. I use them on my PBSF to keep the unit from separating and going on walk about. I only need to change them once a year and the PBSF is on the seat stays low to the ground getting extra wet and dirty and lots of sun beating on them. The ones on my Dinotte are shielded from the sun and seem to last even longer.

Link to the DX Marwi mount for the lazy guy.

YMMV