Marvel Mystery Oil will work wonders...I used MMO recently to revive a 30yr old Troy Bilt tiller...among other things, its throttle control cable was frozen; I used an old squirt can to trickle MMO over the entire cable sheath length and gave it a day to soak in...the next day, the cable broke free and worked nicely with no squeaks...the shop manual mentions applying light oil to the cable and pivot points for its control function periodically, to keep things moving freely, so I have been using MMO from a squirt can once a year for this purpose...as far as spiffing them up, MMO might be a problem as paint does not stick to it, so after soaking the cable sheath in MMO to free up the cable, it'll need to be cleaned off with lacquer thinner thoroughly for any coating to adhere properly...after coatings have cured, then the lubricant of choice can be applied to the cable, but do not be surprised if the sheath finish delaminates a little where it contacts the lubricant