Just as I finished mowing, 1 drive handle would not engage... started it 5 days later and then "BOTH" drive handles would not engage ??? NO OIL LEAKS.... belt seems to be operating correctly... brake arms/cables seem right... as do the hydro contol arms... I dont know how to check the idler pully... it "seems" tight...I also attempted to purge transaxels even though they have never been worked on... Could the belt have gotten too slick, yet still be appearing to spin the pulleys, but not strong enough ??? Mower used 4 1/2 summers.. Please help... any insight is very appreciated...