[Travellingwave]

I suppose a halfway house would be to remove the inner windings and immerse those in a very much thinned down varnish , even better under vacuum. That way you would not make it very difficult to remove again later if a fault did occur.

The transformer varnish I used ( from RS components) seems to dry to an almost caramel consistency to is quite easy to crumble off if needed. Not sure standard varnish would be as easy to remove for reworking if needed.