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outer seal

if the outer seal appears to be bad ( gear oil on the backing plate?), it usually means that the inner seal is bad and the axle bearing is getting soaked with gear oil and leaking past the outer seal and on to the backing plate. If the outer seal really is bad for some reason then you will need to press/cut the bearing off (you will need a new bearing) to get to the seal and be careful not to damage the bearing retainer plate while doing it.