I have these axles on my trailer and need to repair one of the axles ! It is leaking grease out the rear grease seal ! In the instruction manual it makes it sound like you have to use their grease seals , as if they are the only ones that will work ? I would like to know if anyone has experience with changing the seals and if they were able to use over the counter seals such as napa brand ? Thx for any info on this !