I recently picked up an HDJ81 and it was delivered with both inner wheels/tires looking like this.
I did this complete service myself as my "welcome to the 80 ownership" initiation. I think it was more of a hazing!
I watched that video above and a few others (and have the service manual). It wasn't super difficult - but was time consuming and messy. Know that its a two day job going into it and you won't be frustrated at the end (as long as you have all the stuff you'll need - including tools).
I like to rate things on a "Use of Profanities" scale and this was fairly low on my scale (like a 3/10)...
Realize that birf soup has absolutely nothing to do with brake fluid or the brake reservoir...... Birf soup is because the differential oil is being leaked into the knuckles usually due to a clogged vent and the differential going under pressure (due to temperature increase) and pushing the oil out to the knuckles. Usually happens after (during) a long trip.