I only recently acquired a trailer w/ oil bath hubs...but I've had grease hubs/bearing buddies for years before that. With that limited experience w/ oil bath, I still can't see going back, so far, and would recommend finding out/fixing the leak w/ your existing hubs.
if you can't find the leak try to cool off the hub before you put them into the water that will help have you tried new seals , it cured it for me .
they get old an the road grit will do a job on them SID roud:
My old trailer had oil bath, they got milky a few times, but I never had a bad bearing in 8 years, all salt use. A grease zirt in the drain plug wouldn't get grease in the right place. Stick with the oil baths, at least you know when you need to change the oil.
Are your caps all plastic on an ez loader trailer. If so the manufacturer replaced mine with aluminum caps/plastic center no problems since. The plastic ones shrink to much in the cold water compared to the hub.
I wasted my money on oil bath and found out they are kind of a bad idea for a boat trailer. So i went bad to greese not having anymore problems. I also started using marine greese so the water cant break it down as well.
Just my 2 cents