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.

In general, oil seals should be selected in the order of priority indicated in Table 1.
ERIKS type GV (type C according to DIN) is equivalent to type M, but is a heavy-duty version with a double metal casing. This can be a useful solution with larger diameters in more demanding applications. There is also a version of this type with a dust lip; the GVST (type CS according to DIN).
One option is to buy oil seals from specialised gasket and sealing material companies like Polymer Trade Manufacturing Ltd, which is known for its expertise in dealing with gaskets and o rings. These companies not only offer an extensive range of oil seals but also provide expert advice to help customers select the right sealing materials for their specific requirements.