Rolex factory services are recommended every 5 years but the cost often starts at about $600 or more...
My open water instructor was gifted a Rolex Sub by a group of his students years before I met him. When I took his course, he still wore the watch daily, still loved it, but he would no longer dive with it. He balked at the very expensive cost of periodic factory service.
Safe Diving,
rx7diver