We use the National Premium seals on the Mack's I work on. There are two different versions of this seal. One that has the regular spring tension-er inside and one that uses a Teflon "bearing". The regular ones work well unless heated. They fail fast if the bearing is off just a bit or oil is a bit low. They also tend to seep if the breather is restricted. The Teflon one is a bit more expensive but it will last far longer and has a higher heat thresh hold. Along the same topic, When we install new seals we replace the duel lock nut with a new Pro-torque nut. I have not checked to see if they have one that will fit the Half track yet but i am going to try to find out. These are a single nut with teeth cut on the inside. They are torqued in a sequence that sets the run out and a snap ring locks them in place. Takes just a minute to install and remove them and they are reusable.
