Wife's cousin is a GM mechanic, and similar to this, he explained how they game recalls/TSBs. When you have a recall/TSB, it's the same process where the manufacturer comes up with the amount that the dealer is paid to resolve. However, if the mechanics individually don't submit common problems, then it doesn't rise to the level of a recall/TSB and the dealership can bill T&M.

The specific example was a leak that was the shorting out of electric window motors due to rainwater leaking through the window. It was better for him to fix it by cutting up a plastic container and attaching it over the motor & getting hourly for it than it was for GM to tell the dealership "Here's the part, you get $8 to install it when the customer is subject to the TSB"