Yeah, it's a small steel box with the transformer potted in pitch. Honestly though if you see pitch on the inside, you might as well just replace it. You could test it with an ohm meter, but that will only tell you the resistance of the windings. Even if they ohm out in the ballpark, it could still fail upon application of HV. I'm of the mind that these particular transformers are just like old caps. There are only 2 types: those that have failed, and those that will. When it does you'll burn the focus pot, and I was not able to find a replacement for it which means making a non original mod. Deal breaker? Probably not, but avoidable? Completely.
The former owner of my CT-100 took the original one apart with the intention of rewinding it, here's the hole through the insulation that caused the primary to short to the secondary.
