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Balance problem on Onkyo TX-7530 Quartz Synthesized Tuner Amplifier

Hi, I own an Onkyo TX-7530 Amplifier that has worked perfectly fine for the last 25 years. Recently, the left balance doesn't seem to work anymore and there goes its great stereo.
I opened it and cleaned it up because the dust had accumulated and I tried different combinations so as to make sure that the problem doesn't come from the speaker terminal.
Therefore I'm guessing the problem comes from the resistance on the back side of the balance knob. It's a part of the pre-amplifier pc board by the name of 'Balance R451'. The thing is it doesn't seem rusted nor borken or burned and I'm not really keen on trying to disassemble it without being sure that part is the problem.
Could the problem come from anywhere else ? Did anyone have the same problem ?

Thank you for your help ^^