You don't need to identify it. There's only 2 seals on it. One on the pto input shaft. The other behind the pulley inside that guard.
Take the guard, belts and top pulley off. Then dig the seal out. Probably destroy it in the process. Then either measure up or take it to a bearing shop.
I don't really understand why anyone would be shocked that a genuine part is significantly dearer than spurious.
In 15 years mending and trading machinery I think I've only ever had to use a main dealer for parts 5 or 6 times. I consider them the final option rather than the first one