The cruise control on my '99 NB recently started "wondering" between 8-10 MPH over the set speed to 2-4 MPH under the set speed. I found a Miata Technical Service Bulletin that recommends replacing part #NC12 06 320 with an upgraded module containing a heavy duty transistor. Trouble is, that is now an obsolete part no longer available from Mazda. Can anyone recommend a reliable source for used Miata parts?