Thanks for the advice! Yup, it was very easy in the end - I took it all apart and found some of the plastic tabs around each dial had snapped off (which explained the rattling), so repaired those, replaced the burnt-out LEDs and polished up the glass.
After that, I reinstalled it all and... no dash illumination, argh! Seems something has gone awry.
I did clean up the rheostat too during my tinkering, but seems like something is still amiss with it. I also realized that the reason it was electrical taped up is because someone had already bridged it with some extra wiring. I've not messed around with an instrument cluster before so wasn't aware that the wire was an extra until I took a closer look.
Anyway, a couple of questions as a result.
Is this spring (see image) supposed to just sit in it's trough and only be attached at one end, or should it be fixed to something at each end? Mine is currently attached at the end with the metal fixture. The knob should then run across the spring in it's trough fairly smoothly if it's all operating properly I assume..?
Secondly, I assume that if I bridge these two pin connectors with a wire the dash lights should work at full brightness permanently, correct? I want to get the rheostat working but it's useful for testing of course!
Thanks!