Tman: That is known as "hydro creep". As for fixing it some people change the fluid and filter and it goes away. Some have to take the fender deck off and adjust the linkage to get it to stop. Then there are a few that has done both and it still will creep a little. Good luck.............. My self I did both the fluid change and tweeked the linkage some but it didnt fix mine completely so I just learned to live with it......