Don't replace it unless the bearings are completey gone. Pull it out, Its probably just sticky, clean it out with some kero or something, make sure it slides up and down under its own weight, put a couple drops of oil on the shaft and you will be good to go. Also just try a transmission reset, put it in neutral in 6th at full revs, let the pedal right out for a bit and then try it in drive.
I'll give that ago for now and see what happens. Phoned local mower shop and they have 1/2 dozen variable speed pulleys there as they say they are pretty common. They are $115 and don't really have the money at the moment to do that especially if that isn't the problem. Transmission reset doesn't help. Mower only runs in 6th gear and that is pretty slow. Eventually stops. Runs ok until it heats up (say 5 minutes). I just thought that the pulley would be worn out so the belts are slipping on the pulley???
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