Rear brake/differential water logged?

[captainspeky]

So after over 2 feet of rain in 2 months, my van got stuck in the muck under a car port. More rain and the rear drivers side wheel was submerged half way up the drum for a few weeks until it dried out enough for me to get it out. Once freed, the van seemed fine, but after driving a bit there was a roaring noise coming from the differential/brake area. Someone suggested I repack the bearings, but the wheels seem to turn freely and didn't make any noise. The rear hub seems like a bit of a chore to get off, so if the bearings aren't noisy I would rather avoid that if possible. Removed the rear drums and sprayed everything with brake cleaner. I changed the diff oil, it was brown and a little frothy like Guinness, not sure if that was due to moister in the oil? Put some 85/140 synthetic in the diff, but it's still making the roaring sounds. Maybe the diff noise is just coincidental, but I'm curious if water could have made it past the wheel bearings and seal, got trapped, then moved into the axle and into the diff after the van was leveled??

http://i40.photobucket.com/albums/e215/captainspeky/van/IMG_20180731_095811_zpsi9p4dmmu.jpg

[Burntboot]

While I wouldn't expect it to make it into the diff housing proper, I could easily see it taking out the wheel bearings.

Easiest way to tell it get it (securely) on stands or on a hoist and run it in gear and, using a stethoscope, listen to the wheel bearings and pinion bearings separately.
It's the only way to know for sure.