Hiya Ian, I own a few Wheel Horses and have (so far) not had the problem you have, so sorry i cant help you...
But Im sure the great guys at the RedSquare Wh forum will be able to answer your question and any other WH related questions you might have.
Here's the forum link for you.
http://whtractor.15.forumer.com/index.php?s=2cb1908418af8d87517f4d87e437d5c4&act=idx
Happy Wheel Horsing
Cheers
Ian
Ian
September 2008