this is standard procedure nowadays, Jensen uses the same stuff,
wax is great but the air dry epoxy is a lot less hassle,
only complaint is you are not supposed restrict nickel lams as it can cause distortion, but maybe the input level is too low to matter,
Ollie sent me a V76 input and i asked him if i should varnish dip it, as it had nothing around the windings, he said "please, no potting compound!" and explained all about magnetorestriction. if you look at all the V series transformers, most do not have any type of compound used except the varnish used on the discs. but the core stays pretty much naked.