I've found some details that suggest that the 8EB2C1B should have the following characteristics.

Input coil DC impedance - 800Ohms (I measure about 57Ohms with multimeter).
Output coil DC impedance - 2500Ohms (I measure infinite with multimeter).

The site that I've used to get these details is (http://amps.zugster.net/tools/reverb-decoder)
and another site seems to agree that this is what I should be measuring (http://www.about-guitar-amps.com/reverb_tray.html).

Can you confirm what the DC impedance I should be measuring is?

If I'm measuring infinite resistance at the output does this indicate a problem with the spring unit or with my measuring technique?
(I've measured at the phono jack and directly at the coil removing the plug that attaches the phono jack socket to the coil with the same result).

Is this unit broken? If this unit is broken then there is no problem, -I'll buy a new one and I understand that nothing lasts forever!, but what I'd like to know is now common it is that the unit would fail in this way, and indeed if the unit has failed with a break in the coil would this likely be from defective circuitry elsewhere in the amp causing undue stress on the coil? (what I mean is can I just plug in a new unit, or is it likely that this will break also).

the amp is a Fender Blues Junior.