[Arran]

The lamination's probably did have some sort of coating on them originally, but then again it is pretty old, it looks like they may have used gun bluing on the metal instead, which is a form of oxide. Transformer cores work better when the laminations have some sort of coating on them, it prevents the core from becoming saturated as quickly. I think that if you could probably leave a sheet or two out when you reassemble the transformer and it wouldn't hurt anything. Trying to rewind a coil or transformer is one of those things that intimidates me, other then one of those Philco RF coil primaries, too much wire and too many variables.
Regards
Arran