Jaco used Petits poly poxy which was a an amazing product but so lethal the US government pulled it and they'll allow almost anything. I was in Florida in the mid-70's stumbled upon it at a marina and refinished two old Fender bodies. You could apply this stuff with a brush with amazing results. Though I do remember the smell was hair curling. I heard Jaco applied this on his fretless neck with a brush.
I have a 66-P bass I defretted and shaved down to be closer to a J-bass width. I've decided to coat it with some type of resin but haven't decided which. I keep reading about super hard surfaces players are afraid to wear thru. I don't think there are enough hours in the day to do that type of damage. Plus you fretted hand should have a lighter touch. I'm still searching.
