Wheel cylinders were both replaced with the rest of the brake sytem. Both looked fine when I took the drums off. The left one must be moving or I wouldn't have gained firmness in the pedal when I adjusted the pads out.

The oddest part of the problem is that it goes away after you drive the car and use the brakes a few times. Then a little while later it develops a vibration from the right when braking.

Note that I have driven this car the last 2 summers on the current brake job without any issues. This has only been a problem since I started driving it this season. So something happened during storage over the winter.