This is where markthefixer needs to chime in. He probably has a source and part number for a replacememt...
You got lucky I was passing through and it caught my eye - I'm off to my dad's house again today (till 10 pm last night) to continue prepping it for eventual sale.
First try lubing/ cleaning the motion transfer bar interconnecting the phono. tuner and cd/aux buttons.
Pioneer treats it as one assembly, aad-559, and it is unique to the a-60.
The mm / mc lamps DO that (on purpose) - the only way they are depowered is when all three function knobs are OUT (none latched, fiddling can get you there). If they were both out, the phono. tuner or cd/aux lamps could NOT light. Now if MM and MC are BOTH on, that means the mm/mc switch is of a high enough resistance to not have the desired shorting function.
I do not know what mouser part number could even sub in. Haven't worked on these much. And until dad's estate is settled and my own life settled down again, I won't be... basically I am on hiatus.