Most manufacturers will recommend semi-annual or annual inspection of caulking at seams and openings, with repair or recaulking as indicated by the inspection. How often it needs to be replaced will depend mostly on conditions of exposure.
I am having a hard time envisioning a need to remove corner moldings to recaulk. Even without removing them, the job can be a pain, it takes a bit of practice to develop the skills for a neat job. Some owners put the matter behind them, permanently they think, by taping (Eternabond is one brand of long-life tape) rather than caulking, and that may or may not involve some disassembly, depending on what you want in the way of appearances for the finished job.
So far I've done OK with caulking over the old seams, which is what most shops will do.
