Oh, yeah..., they are separate components no doubt about that, just like I assumed they would, they are called linear potentiometers or slide pots. I'll give them a good cleaning with a contact cleaner, if that doesn't solve the issue with the Upper1 slider, I'll swap it for another one that I don't use as much, or I'll try to find a replacement linear pot...

I don't recommend anyone to do this type of work themselves, unless they have experience with electronics, otherwise things can get damaged very quickly...

The 10 linear pots have a marking on the side >>> 248C-10KB <<< , without checking the resistance on them, going by the number I assume it's a 10K Ohm pot, will see, I'll need my DMM for that.

Wish me good luck! I wish I had that service manual, anyone has it, please share.