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....