We have the drive units in stock, 6100.700, (order on Tunze.com) Premium Aquatics also stocks most spare parts. However, it is likely best to send them in to be checked out instead of spending on a part that may or may not solve the problem. Just include a note with return address and phone number in the box and do include the power supplies-
Tunze USA
305 Victor St
Austin, TX 78753