The grooves in brass cam are machined not wear. I do not know about the Wobbler. Brian Wilcox makes them on an exchange basis due to metal parts embedded in the Wobbler.
If I were forced to Walk the Plank and make a guess, it would be the grooves in the Oscillator (Hockey Puck) are part of design to trap water between brass cam and rubber oscillator to lubricate both and reduce wear. especially when operating in shallow water where sand and silt are part of the mx. My best guess anyway.
Louis
Just ordered a wobbler from Brian a few minutes ago!
Prepare to be boarded!