i have had a problem with stripping the nipples while truing wheels in the last two wheelsets i've attempted. in both cases, the wheelsets were previously owned and were partially stripped to begin with. my question is how to true the wheel when that particular nipple is stripped? i know there are spoke wrenches that have the 3 corner grip, but i am currently using a park 3 size tool with square grips. is my only resort to remove the tire and use a flathead and go at it from the inside of the rim? should i take to shop to save the hassle?