The Oriole's did stall for a bit while studying an MRI last year. Signed the 21st but the delay meant he didn't technically sign until the 25th of Feb.
The biggest difference I see between his good years and bad is in pitch usage. Specifically in his 4-seam which he threw around 60% in his good years (at 92-93.5) but around 30% in his bad year and a half (90-91.5). More generally he been using his Change, Sinker and Slider more, 4-seam and Curve less. The pitch values don't seem much different between the pitches except the 4-seam, which has remained mostly the same throughout. His usage and effectiveness with every pitch has changed year to year what seems significantly to me. He didn't have a sinker through 2010,for instance. His slider has gotten worse and worse as he's used it more and more. Check his annual BA against by pitch type and the slider bar has gone up and up throughout his career.
I haven't studied these a whole lot, so maybe I'm reading too much into it. You tell me?
Edit: Just noticed Jeff Zimmerman mentioned the idea of a move to the Pen: http://www.fangraphs.com/fantasy/mixing-fantasy-reality-trades-adp-proje...