I have a 1997 proline dump trailer. It is rated for 12,000 lbs gross. Empty the trailer is about 3500-4000. The other day I weighted in and out when I picked up some pea gravel. The gravel weighed 6,000 lbs. When I went to dump the gravel the pump started up like it was going to start raising the trailer but after 5 seconds it started making a clicking sound and would not lift the load. I had the battery checked out at autozone and they said it was still good. So I am guessing it is the pump. Should I try changing the oil? What type/weight oil do the take? Any other ideas? It is only a single piston design.