Lonny,
If you were using the split washer with a stock spring and stock disk, it probably was one of the contributing factors to your clutch going out. The split washers exert quite a bit of outward force on the pressure plates and the stock spring is pretty marginal anyway. For plowing and other yard/garden work, I would recomend that you use a fiber disk with a blue (color coded ISO die spring) and put a little more preload on the spring than normal. Also, the fiber disks are not much thicker than the lock washer is when flattened. So, the washer may have been bottomed out and holding the pressure plates apart. A split washer with the fiber disks really isn't benificial. It is just about a necessity with the aluminum disks.
Todd