Electric Trailer Brakes and Gain Caused Wear

I just finished replacing all my brake assemblies (eTrailer) and still have to take it down the road to completely seat them. Your brakes (if Dexter) should be self adjusting and that shouldn't be an issue, especially since you've had them for 4 years. You don't say how many miles you've got on them though. I replaced ours after 30k, but they and the magnets were only about 1/3 worn - one had a bad seal (from a Virginia safety inspector manhandling the drum off & on) and had gotten grease in it. I only noticed a decrease in braking while we were on our way back from CA last year. Usually ran at about 7, but had to put it up to 10. Unless you've around 50k miles, I doubt the brakes are worn out, but I wouldn't be surprised if you've got a failed seal or two. Seals are only a few bucks each and it's not difficult (although messy) to pull wheels and drums to see what's going on. If you've a seal or brake problem, the whole assembly is only about $83. A complete drum with new bearings is a whopping $82 as well. If you're not doing it yourself, don't get taken by outrageous parts prices.