Odds are there's nothing missing and its a crude variable capacitor, with a value of a couple of pF, adjusted by bending the small pin towards or away from the big pin. If there *was* something missing, you'd expect to find debris rattling around inside the screening can + traces of the component body on the pins.
* Have you checked the modulator video input and 5V supply?
* Have you got a TV win an analog tuner that covers UHF channel 36?
* Have you checked its output on a UHF spectrum analyser?
If there is no UHF output, odds are its a dry joint on the undeneath of the modulator PCB. The modulator would need to be desoldered from the main board to gain access. Worst case, if the video in and supply are OK, and the modulator is FUBARed (which I doubt) you can probably substitute an Aztec UM1233, which are much easier to find as N.O.S.