What AussieBlue is trying to explain is that the LCD segments are electrically connected to the clock circuit board by 2 carbon/rubber contacts.
Much like the problems that ppl have with the Nokia's, if there is not sufficient pressure to hold these contacts FIRMLY on to the Board, then parts of the LCD Display mysteriously disapear, causing a garbled display, much like what you have now.
The carboard would help keep some pressure on these rubber contacts, ensuring that there is an electrical connection between the Board and LCD Panel.
Anyway, EF/EL Clocks cost about $100 from wreckers.
A better option might be getting a Trip computer from the Wreckers. (The cost of these range from $150-$250 from wreckers).
As a very minimum, you will need to run at least 1 wire from the Original Clock plug, to the instrument cluster, to get the Trip computer functioning.
You will need a further 2 wires to have the Trip computer buttons, and side lettering to light up at night.
This is a very easy mod, as a friend added a trip computer to an EF Ex Chaser running LPG, and the thing works perfectly !
Anyway, just some idea's of what U could try !