Yamaha grizzly 600 belt trans problem

I have a grizzly that has had a problem with the belt trans.  The bike had some problems pulling out and at low speeds, kind of acted like a torque converter with a high stall speed it seemed worn on the belt and some of the other parts associated.  I had planned on upgrading to a high performance belt and pulley/ spring system.  During the teardown I noticed a very small amount of oil around the seal on the output shaft of the engine. Like I said its a very small amount of oil, but I am not sure how big a deal this is around the belt.  Anyone know if I should tear the motor down to replace this seal or just let it go?