Yes- the rubber deal is a boot or socket of sorts. It slips over two pins on the lamp board. Remove the old lamp & boot from the board, then remove the lamp from the boot. - I just usually pull on the bulb and the wires follow. You'll figure it out. The wires for the new bulb go through the holes down the middle of the boot, then back up through the outer holes, which slide over the pins. Small needlenose are helpful. Kinda like threading a needle.
On your missing channel in stereo - good chance dirty switches or pots are the cause. Cleaning is where I'd start. I use Deoxit D5 for the switches and Deoxit D100 for the pots.
The meter lamps are supposed to be 8v 300ma, I don't think you'll find the original style.- I use 8v 250ma wedge lamps, they are about perfect. - WJOE sells those also.