Does the OT work now, only it's not stock?
It might be one of the universal replacement 100 watt transformers or similar that New Sensor sells along with AES and most every tech uses for repairing twin/dual showman/quad reverb .. It could be that the transformer will work fine, only the right output wire needs to be connected to the jack so the impedance will match the pair of speakers. I think another post above mentioned the combo speakers wired in series for a 16 ohm load? If so the speakers rewired to parallel for a 4 ohm load matched with the 4 ohm tap and you're good to go. I've got one of those OT- the output wiring is black-common, white-2 ohms, green-4 ohms, green with yellow stripe-8 ohms..
There's a spray that I used on my car when I lived in frozen salt world, they sold it at Advance auto parts or maybe it was Home Depot; made by Loctite the product is called 'Extend'. It's a thin clear spray that reacts with rust (chelation) but is clear on everything else. It turns dark when it reacts with the rust.