I'm getting ready to put my d310 back together and ran into a issue. I'm trying to figure out with sleeve o-ring to use. The engine was put in this tractor years ago, it was a short block from Abilene machine. The instructions that came with the piston kit have a list of model and serial number to go by for which o-ring to use. Well I don't know what model my engine came from... and neither does Abilene machine. My serial number is 310DT2D080514. The o-ring with the yellow dots is 4.75mm thick and used after 1979 and the o-ring with red dots is 5mm thick and used thru 1979. Anyway to determine which one to use? I really want to get it right the first time.