correct, rust converter. try the brand name "Ospho" if you can find it. chip out the excess rust with a scraper or wire brush, apply rust converter then after the color turns black (after about 30 minutes) you can paint over the treated part.

kung wala ka makita na rust converter then you have no choice but to wire brush the affected area until all you see is shiny metal, then apply cold galvanizing paint (may nabibili nyan sa ace, "Zinc-It" ang name. just one thin coat. let dry for a day before applying paint (preferably spray paint, don't use a brush).

pwede din aluminum paint kung wala ka makita na "Zinc-It". but aluminum paint does not prevent rust from starting up again if you miss a rusted spot. zinc will since it has galvanizing action.

is the affected part the rail where the car seat slides for adjustment? then the best is to apply a thin coat of grease. see if you can find the electrical insulation grease (it does not smell!). color is transparent so it does not look like grease. it's made by Dow Corning, in a green box and green tube (parang sa toothpaste). O-ring lubricant also works very good (parang transparent grease din yun, made also by Dow Corning, so green box and green tube). it also does not smell like ordinary EP2 grease do.