Hi, thanks for the quick answer!
I've tried to re-bend the pins, clean them with IPA, and also swap places with the 2nd button slider, but nothing worked (2nd button turbo works perfectly with any of the two sliders, though). It looks like the bottom pin of the capacitor connects to the bottom pin of the turbo slider, so maybe the cap could be the culprit?
I have to say that I'm a complete newbie in electronics, I know what a resistor and a capacitor are, and I've been soldering guitar cables for many years, but I don't know if a failing cap could lead to a carbon contact not working
I've included a couple of links to pictures of the board in case they are of any help.