i have a zd28 that the left wheel will barely move. I've read that there are problems with pumps or something with these. Is there anything that I can check or do to test this or figure out the problem for sure. I've looked and the rods going to the pump are moving the same....the left and the right. the right works correctly but the left hardly has any response at all. Also is there somewhere that I could download a service manual for this for free?