My brother just bought a Toro GTS 4-stroke self-propeled walk behind used mower of Craigslist for $75. He checked it out before he bought it and it seemed to run great but the self propeled drive was kind of come and go and the adjustment was as tight as it goes. Well he moved his front lawn 1100sq ft. with it and it did alright. When he went to go do the back yard the belt as well. Shoudl he just replaceblades would not engage?? Are the blades driven off a belt as well? Should he just replace both belts becasue of there un know life.