I do not feel that Britton is overly concerned about the overall saves record per se. If anything, it probably stems from his earlier oblique injury that affected his delivery in some fashion. That, or physcologically his mechanics have changed somewhat in an attempt to not put strain on the oblique and reinjure it.
I agree the spring training injury has to be one of the big reasons for the rust and lack of control. The problem is that the two guys who created Zach Britton the all-star closer (Wallace and Chiti) are long gone and not around to fix Britton's mechanics. Before they came on the scene, lest we all forget, Britton was a marginal bullpen guy and failed starter.
So yeah I'm worried a little. Zach has had a heck of a long run, but bullpen guys are like fragile eggs. They can fall off the map in an instant. Like Jim Johnson. His sinker went north and his career went south.