Generator Stator Clean Up

How did the rotor fail? If it was a significant failure, you may have a fair bit of melted copper scattered through the stator winding - which is not going to be good in the long run.

Having the varnish build up in the air ducts (if there are any) is a no-go ... those airways need to be kept clear to allow proper thermal transfer from the winding. Getting in/around the slots and teeth (and presumably winding) is not an issue ... as long as you don't leave drips and drabs hanging in the airgap between stator and rotor where it can get broken off.

The likely reason there appears to be little varnish on the existing stator winding is because there is no material there to absorb it. An enameled strand (which is what you probably have, in what is called a "random" winding) has no textured surface (think cloth) to hold the varnish. It just drips away if the varnish is too thin - or collects in lumps and bumps if too thick.

Your "varnish" is going to need to be compatible with the rest of the insulation system too - which might mean a bit of investigation is in order. If you have a manufacturer and/or rating for your equipment, someone on here might be able to tell you what was likely to be used the first time around.

Converting energy to motion for more than half a century