Flyback with Missing Insulation

[PredictaNoob]

While inspecting the flyback transformer from my Predicta Debutante (10L43), I found a 1/4" or so chunk missing from one side of the flyback. It doesn't look burnt, it just appears that the rubber dried, crack and fell away.
I've read where guys have removed all of the rubber then sealed the windings airtight with silicon (I assume a high temp variant?).

Can anyone describe a good technique (assuming that this flyback is still serviceable) and what products you used? Thanks!