My 2006 c series keeps losing its rear wheels to front wheel relationship. I can straighten them out as you should to drive in two wheel steer, but when you try to use all wheel steer it starts crab walking after a couple of minutes. I noticed that there was a little oil leaking out of the rear steering shafts, enough to see it on the cylinder not on the ground. Could this be the problem and can you just replace the seals?