The rubber drive wheel on my T7 keeps building up rubber compound on the motor shaft causing slippage. I have to remove the honing wheels and clean the motor drive shaft after approx. every two to three hours of use. Use is "not" continuous, 2-3 minutes here, 5 minutes there, etc. I have sanded the rubber drive wheel as suggested in other post, but it hasn't resolved the problem. How do I obtain a replace under warranty?