Yeah... no, the idea that your equipment can permanently break based on a % check is insane imo, it would cause so much stress on the player's part. It should be that, imo, the lower your skill in repair, the lower cumulative amount of repair per click. Obviously, the higher your skill the higher the cumulative number. So say your sword has 20/50 durability, and your skill in repair is 1, each "repair" you do to the item is an rng between, say, 13-17. At repair 2, the % increase is something like 20 or 30%, so that is a 16-20 repair.
Better yet, you may find a "golden hammer" (remember this is a Divinity game, comedy/silly elements are allowed) that ignores your repair skill and allows a straight-up 100% durability heal, but it's a one-time use item. Alternatively, you could just sell the golden hammer for money, buy a bunch of normal repair hammers, then get more exp.
