Two years ago purchased a front drive 21" mower. Whenever you use it, dirt and other stuff gets in to the belt pulley drive for front drive and makes it slip badly.
The rear drive unit has a guard over the belt pulley at ther blade, but our front drive unit doesn't. Sears offered to repair it, which they did; and within 20 minutes of starting to use it again, it started slipping.
They offer to repair it, but our warranty runs out this spring. They won't admit that the design is flawed; but if the rear wheel model has a shield, why doesn't the front drive model??
Review about: Sears Repair.