I recall trying to find lamps for in the speedo, they are a different bulb than those tiny dash/ ashtray lamps. i went to a local parts store and he was nice enough to let me go through his collection. i found some similar but the socket would not match and the wires are stainless so I couldn't solder to them.

what I did was took a fine strand of copper wire, wrapped it around and around the stainless steel bulb leads, folded it over, and soldered that. I know it didn't actually solder to the stainless steel wires but because they were wrapped around a whole bunch of times and the copper is tinned with solder, I felt t made a good reliable connection anyway.

id jumper the thing, If you want it dimmer you can add a resistor and it's easy enough to put your meter on ohms and to the two wires and measure the resistance. if you want to try a spray cleaner , deoxit is a good one. you might be able to get some inside the pot or drill a tiny hole to get some in there.

the one in my 122s is pretty bad, I just play with it and get maximum brightness,
it seems common for the potentiometer to go flaky, it's likely just dirty in there.