Well here you go... take it for what it's worth! I found an old Conley 120 folder. The bellows looked like a spagetti strainer. In one good sized area I coated it with the black finger nail polish. Another area I did with the liquid electrical tape. The black nail polish goes on smoothly and flat with a small paint brush, it filled the holes very well. Later you could close and open the bellows without new light leaks.
I then did the liquid tape, even with a small brush it went on thick and lumpy, definitely looks like a patch job. It does seal the holes, but makes the bellows harder to open and close.
Personally I will be sticking with the nail polish. Then again, to each his own.
Good luck on your choices, some also recommend gaffers tape.
I even read where back in the day press photographers would locate the nearest shoeshine boy and "borrow" some of his black shoe polish while on assignment....
Patching from the inside, I applied some liquid electrical tape, and then I folded the bellows and wiped off the excess a few times. Seems to work it in really well... It's doing a brilliant job so far, and from the outside of the camera it's impossible to tell. It doesn't seem to be making the camera any harder to open, but i'll have to wait for it to dry completely. This stuff is just the ticket for fixing my 8x10, we'll see how well it works on a camera that folds it's bellows very tightly soon...