There are two different seals. One is virtually the same as the original, while the other is more like a modern seal with a flat flange,
Both should work if the input flange is not worn. Before blaming the seal itself, check that it is not leaking around the splines behind the pinion nut and also check that the differential vent (this doubles as the bolt holding the brake fitting in place) is not plugged which will allow pressure to build up in the housing.
If your input flange is worn, a speedi sleeve can be installed over the worn area. D25s use a spicer joint unlike the USA built cars... in case you were thinking of replacing the input flange.