Water will always settle to the bottom, pretty much immediately, but it will take a while for it to displace the film of oil on the case.

Flushing an assembly with bearings is tricky as you can wash dirt INTO the bearing just as easily as wash it out. More so in my experience.

If the contact patch (shiney or, perhaps in your case slightly rusty) is right in the middle of the gear teeth (lefty-righty and top to bottom) with no sign of galling, blueing or pitting, then the gears are likely set up fine.

Any noisy bearings must be removed for cleaning and inspection at a minimum (with re-pack). Reassembly with existing parts is usually OK. I was disappointed to find that the 27/30 has "sealed" bearings at the hubs. That is they do not share axle oil so they must be repacked from time to time!

Axle end-play is listed in Bently. If it is excessive, take the whole thing to a good 4x4 driveline shop (preferrably that specializes in axles) and ask them to "freshen" the unit. They have the experience to do it right and resources for parts I haven't been able to match.

ANY lateral slop in the shafts or pinion is bad.

Mike!