Re: Why you should rinse your brakes.
That trailer looks like it hasn't been maintained in years, even for salt water use....Drum brakes are a problem, even with the flush system, because the dust boot for the wheel cylinder is not water tight. Then water gets in with salt crystals and seizes the piston. When they are new, I take them apart and put synthetic brake grease on the piston and pack the area under the boot with grease, as well as the hole where the push rod enters the boot. That keeps the water out and the cylinder from seizing. The next time I re-do them I will try sealing the edge of the dust boot with high temp RTV for an even better solution....
The other part that causes trouble is the adjuster, these are not stainless so they rust and freeze up. I extend the adjuster all the way out and then pack the threads with OMC triple guard grease which does keep them free.
Disc brakes are better in design for sure but you can still have problems with the caliper pistons seizing in salt water....Of course they are a lot easier to service...but where I am there are many steep hills and drum brakes at least have the return springs to reduce brake drag, and since they are freebacking, no worries with the back up solenoid failing....