I’ve been riding an oracle 24 quite a bit lately, in our local tech trails. I would most often come back home with the uni covered in mud and usually rinsed it with a garden hose before putting it away in the garage.
The uni is only a couple months old, but now both bearings have a “gritty” feel to them when I rotate them by hand. The wheel doesn’t “freewheel” the way it should either. A couple of times, I found that the wheel would actually resist turning the day after a ride.
I have new bearings on the way. I had assumed that rinsing the uni was OK; it appears not - lol.
IMHO, rinsing the mud off is probably a good idea, but it will also rinse the oil/grease out of the bearings after a while. Since the bearings are typically non-plated, they will rust pretty quick. I would recommend spraying the bearing area with WD-40 after hosing off the mud. That will displace the water and prevent rust. In any case, off-road muni through mud is going to be hard on bearings, so you should probably get two sets while you’re at it and save some shipping cost. You will most likely be doing it again in the not-too-distant future.
Those bearings aren’t really intended for wet and muddy service; the seals are mostly for dust, and there probably wasn’t all that much grease in there to start with.
But it’s pretty easy to pop off the bearing seals with something pointy, clean out the gunk with some solvent or wd-40 or whatever, and then regrease them and pop the seals back on. Goodbye, grinding noise!
Taking the cranks off gives you easier access, but it’s not necessary. I pack them full using waterproof marine bearing grease that I bought from an auto parts store years ago, a few dollars buys you a lifetime’s supply worth.