EDIT: Just reread the op's post where there is "gunk".... that would be cause for checking them out. Below is just my "general" experience with NO gunk/oil getting out. Two years ago, I pulled the rubber plug on my Dexter and nice, clean grease was there to meet me. Also I adjusted the brakes
with NO apparent oil/grease prevalent. That's was the clincher on not pulling my wheels.
7 yrs on a 13'er with NO repacking. I spin the wheels and listen- got to be able to separate the "brake" scrubbing sound. I do the "play" test from side to side. The bearings still feel perfect. I pull for several miles up to at least 60mph (apx 20 min) then pull over and check the hub temps. I do this when it's cloudy or late evening as the sun can affect the temps. If I'm on a longer trip...after 75 miles or so. If they're normal, I keep trucking.
I know what my hubs felt like from the factory and can always compare....I keep pulling.
Why? Because my trailer is light
based on the actual axle
capacity so I dont worry about it.
I would have them checked by a professional if you have ANY doubts. What I described on how I do it, I do NOT recommend this for anyone. It's just what I do and believe in and it works. If I was getting ready to travel across the US, I'd do a bearing pull/inspect/replace and/or repack. Most of my trips are under 100 mile hops on back roads. And I never pull over 60-64 mph avg.
Look for "dry rot" on the tires
. This almost bit me!