I had the same issues with the rubber donuts. Tossed 'em years back. Now I use lengths of electronics heat shrink tubing as plastic sleeves on the cables. I don't shrink them though. Just leave them a sliding fit. This way you can use the same sleeve for years and multiple cable replacements. Cheap, come in various colours and easily fitted. The 1/16 size works for shift cables and the 3/32 for brake cables.