Slipping Mower Belt

[Guest]

I seem to have a slipping mower belt on my 20 year old 5210H Simplicity. The mower deck is a 42 inch model. When I sit on the tractor with the mower engaged, the noise that comes from the mower leading me to believe that it is slipping is coming from the pulley on the left hand side (as you face forward sitting on the tractor). Any suggestions. I'd love it if you could direct me to a diagram of the belt and the pulleys. The manual leaves something to be desired. Thanks.