Just checked my brake shoes and notice grease inside the hub and drum assembly on the left rear. No dust at all in the assembly. The right rear side was full of dust. I suspect it to be the oil seal. Only have 90k miles, is this a common problem at this mileage? Any advice will be greatly appreciated. Also, is it very difficult to change the seal? I have a shade tree Mechanic and a repair manual to go by. Thanks.Mohok