Last night I decided to remove the terminal blocks from my F125T12 fluorescent tube and while doing so, I accidently broke one of the pins off the endcap while trying to pry the terminal block off because the screw was rusted.
I can confirm that the tube has not lost vacuum and can technically be started with a plasma globe or tesla coil with the missing pin.
My knowledge of how fluorescent tubes are made is enough to tell me that the tube may be fixable if I could somehow remove the endcap and splice in the pin from another tube and hope that it works.
I may also be able to remove the black spacer and access the broken wire through the hole where the spacer sits.
Any ideas on how I could try with fixing it?

Update:
I fixed the pin by removing part of the spacer so I could attach a brass crimp connector to the cathode filament wire which was thankfully still intact.
I squeezed the other end of the crimp connector with pliers to create a pin, created a new insulator by cutting the end off a rubber wire cover and taping the whole thing in place with some cleverly cut bits of packaging tape.
A quick test fit with a tombstone lampholder told me that the makeshift pin is strong and sturdy enough to rotate the socket and lock into place!
I normally wouldn't go to these measures to save a fluorescent tube but this was an exception because the tube I fixed was my GE F125T12, the only 8 footer in my collection.

For your next pin repair, try liquid crazy-glue (shove in a piece of cut paperclip) then liberally sprinkle some baking soda over it. Watch as it hardens to steel.

I usually fix my tube using doner end cap and and use high temprature hot glue the cap in place.