Thank you for your recommendations, Mr. Kevin.
I´d gladly ship these wheels from Lisbon. From what I saw in your fantastic website I´m sure they would return in great shape! But at the moment I don´t think it´s worth the hassle. As English is not my native language, if it sounds too complicated it´s just me trying to make myself as clear as possible.
Nevertheless it is great to hear from the Master, and an honour.
OK, back on topic:
I disassembled the pot and cleaned the contacts with isopropyl alcohol and cotton swabs. After reassembling the glitch was still there, so the wafer must have weared out.
Instead of replacing the entire pot I´ll try to replace just the wafer as the metal shaft was shaped in a way as to keep the hex screw in place, preventing the wheel from falling off. This seems like a bit of overengineering, though.
About the wheel, there´s a small crack around the opening, but it´s nothing serious and it´s barely noticeable.
I´m more concerned about a yellowish colouration of the wheels and how to remove it. Is this common? Is there any automotive spray paint everybody uses or something?
Thanks in advance.