The Scotty warranty is fine if you're in the comfort of your living room but everyone should at least be familiar with the guts of their downriggers so if you're out on the water, you can self-medicate the problem and get back to fishing.
Jammer's comments are to the point---my guess is, it's crud on the brake plate. It's an easy fix---remove the pulleys and the drum so you can get at the brake plate. Take the brake plate out and clean it. I used very fine emory cloth with lots of soapy water---jelly fish squeajum, crusted salt, all the crap that comes in on the wire or braid is fed by gravity down to the brake. It should be part of typical pre-season maintenance
I made the mistake of applying Corrosion-X after cleaning the plate-- I learned real quick that lubricating the brake plate is not a good idea so I cleaned it all off.
Once I got it all buttoned back up I was back on Broadway, cruising for spring love