Any time you dunk steel/iron/brass into salt water, you've got corrosion. And not all launch ramps have wash downs. So sometimes Journey On's trailer sits without flushed brakes.
That said, I've had less problems with the electric/hydraulic brakes than with drum brakes.brakes. In 6 years, I've replaced one caliper (leaking) and 2 set of pads. When the boat sits over the winter, the rotors do get rusty and the pads have to smooth them off.
If you want good brakes for a C-Dory 25 or Tomcat, electric/hydraulic with disks are the only way to go. Any maintenance is well worth the great breaking.
Boris