[rfeenstra]

External rust is not an indication that the transformer is a goner. You have to check with a meter to see if there is an open winding, particularly in the hi voltage winding. Filament windings will register a very low resistance. The primary, according to the service info, should be about 4 ohms. From either Yellow to Green should be about 260 ohms. If these measurements check out, you may be ok. Final test is to power up the transformer, preferably through a current limiting light bulb (in case there is a short in one of the windings), then check the output voltages on each winding; filament and HV windings. Careful, there is several hundred volts on the HV winding! You say you don't have a way to test. does that mean you don't have a meter? If not, buy one! It is indispensable.