You did say it still rotates so you can continue driving it!!
I suggest you not eat that Mayonaise as it has not been refrigerated.

<snip>

Sludge. Apparently you have some moisture in your oil.  Change the
oil. If it immediately returns, you probably have a coolant leak, say
a cracked block or head or a bad head gasket.

Yes, indeedy. That's why motor oil has detergents: to hold water
in suspension until you change the oil. Oh, and the acids that are
dissolved in the water, too.

I recommend some penetrating oil and a large hammer hit on the face of
the drum to break it free.  Big hammer too.  If the drum is moving in
and out already, then the emergency brake will maybe need backing off or
maybe it's cable is stuck on that side.

I have also seen little star clips on a wheel lug holding the drums on.

The white goo is water mixed with the oil.  That happens in vehicles
that are only driven short distances and is the reason short hauls are
considered 'severe' driving when it comes to oil changes.

If you drive a lot on the highway or long enough to fully warm up the
engine, the condensation water boils off, it has no time to build up and
make 'mayonnaise'.

That can also happen because of a leak of coolant into the engine, but
you would have a corresponding loss of coolant in the radiator if that
was the case.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's