Although highly unlikely, maybe a bent valve that won't go down, broke the rocker? Maybe some kind of notch in the cam lobe? Rockers aren't exactly under much durress (compared to other components), so something else caused it to break.
2000 Cougar V6 MTX
2001 3.0L Swap w/ PnP Heads - It ran, it boomed, it RUNS AGAIN

Nearly all suspension mods
Big ass stereo
...and more...
See Her Here