I can confirm that there is a problem with some of the 6 cyl BA motors, but I don't know what the build number ranges/dates are.
The sprocket in question is the one that the crankshaft position sensor gets its info from (it's not the chain sprocket).
The dealers should have a "test kit" which is basically a small torque wrench set to a specific torque and a small slotted socket. It's applied to a tooth on the sprocket, and if it screws the tooth off then the gear is one of the dodgy ones and they replace it.
BA II XR8
XB Coupe under reconstruction
'85 F250 with Mild 351 Clevo