Does your rear have grease fittings near the backing plate and if so could someone have pumped them full .
Another possibility is overheating bearing or brake drag .
There’s supposed to be a fibre washer behind the steel washer . I know this doesn’t answer your question but it could narrow down the replies and possibles.
It’s been a few years since I put the hub on after doing the brakes, but I definitely put the key back in. I’ve put maybe 5k miles on since then. I did not replace the seal then. It’s possible I packed too much grease in the roller bearings? I do have the grease zerk, but I’ve never put grease through those back there.
I appreciate the ideas and tips. Maybe I’m missing that fiber washer. I’ll take it off and see what’s going on. I also am not sure how the grease got out there.
As Angledrive said above there is a fiber washer under the heavy washer which prevents leakage. I believe your brake hub nose has been modified it may no longer have the recess for the fiber washer.
It appears in the photo that some type of substitute washer has been used instead of the correct fiber washer.
If you don't have the correct fiber washer you can make one to fit out of a piece of leather, like and old belt.