Hi everyone, I'm new here but this thread reminds me some issue I had as a... musician at the beginning of my music journey: how to clean a non lacquered fretboard (ebony, rosewood, etc...)
And yes lemon oil do works ! it's cheap, gentle, and reliable, it really attracts the dust, and if wiped well it won't feel slippery at all.
I've been asking myself too how to clean those old handles, white vinegar, avoiding alcohol as much as possible to preserve the colors, not too much water to avoid moisture, gentle sanding, etc... I've tried literaly all the things you all mentioned here, and nothing's better than Lemon Oil.
Just buy one bottle at a music shop, on the internet nowadays of course, the Dunlop 65 formula is cheap and can be found at any time anywhere, it's the biggest brand worldwide, plus it's easy to use. I'm new so can't post any link for now, search for the Dunlop 6554 Fretboard 65 Ultimate Lemon Oil you'll find it easily. It is the most reliable and safe product.
Pay attention to the wood's pores though: it has to be really opened grain. I've got a Viscaria blade too, bought new and my hands don't sweat, so it's ok still. Its handle got quite opened grain, so I guess it's safe to use lemon oil.
Edit: So now I can post links YAY !
https://www.thomann.de/gb/dunlop_le...iLCJjdXJyZW5jeSI6IjQiLCJsYW5ndWFnZSI6ImVuIn0=