If the windlasses gearbox has milky white oil or no oil in the sight glass (it can be hard to see at times) then I would think that unless its a emergency/temporary condition one would want to make things right rather than just refilling the gearbox with new oil through the site glass opening. There is no combustion going on in there so other than leaking out, where did it go, evaporate? After all in my mind a windlass failure is more than an inconvenience and could be actually be quite serious. My anchor weights 120 lbs. plus the chain, less the buoyancy of the salt water. I would not want to pull that mass manually.
How many among us carry a spare windlass or even a spare windlass gearbox? I don't.
In order to reseal my VWC's gearbox removal was required as you have to split the box. How else are you going to determine if the shaft seals failed due to sea water exposure, bearing failure or shaft grooving? You simply have to take it apart to find out, it's not hard, even to put it back together.
Once apart the failure mode is likely self evident, (in my case it was bearing failure from being run dry for too long) and along with a few new shafts, gears, bearings and seals my gearbox is like new. The obnoxious part is having to pay $50 for the kit of glue/gasket goo (not bought from Maxwell) that seals the box back together. it does a good job but I've got likely enough of it left over to do the same thing 3 or 4 more times that will be stale dated soon. Oh joy!
Take it out and apart and fix the problem while it's easy for you. Your back, your wife and your insurer will appreciate your thoughtfulness.
