Rubber type
Ethylen-Propylen-Dien-Kautschuk (EPDM)
Thoroughly clean the sleeve at the back of the pulley, and look for any roughness on it where it touches the seal. If necessary, smooth it with fine wet-and-dry abrasive paper.
What is Oil Seal | Purpose , types of Oil Seal , Advantages
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Some disadvantages of NBR are poor ozone, sunlight and weather resistance as well as limited high temperature and flame resistance. For higher temperature resistance, a much better material to use is Silicone.
Types Of Oil Additives
Oil seals come in a wide range of types, and they also have various sizes.
When selecting the right oil seal for your machine from among these many varied types of oil seals, the following two criteria are very important.

To ensure correct fit and proper protection against contaminants, the inside diameter of an oil seal must be slightly smaller than the shaft diameter.
Standard 3760/3761