I'm not sure, since I've never taken an Intellivision 1 unit apart. I don't know how the wires are attached to the motherboards, and if they can be replaced like an Odyssey2's 'built-in' controllers can be.

I think the easiest thing to do is get a replacement console. You can get replacement controllers for an Intellivision II, and the Sears Super Video Arcade, those consoles would be preferable to the Intellivision 1. Although the Intellivision II won't play many of the Coleco games, which might be a bit of a blessing.