from post 14 "or most likely a broken compression release." which is what you have. my guess is that the threads are pulled out of the head on that one cam cap. remove the exhaust cam & check out the caps & cam journals and the holes. be careful... each hole has a dowel that sometimes falls out & can go into the engine (I Locktite them in). you may be able to Helicoil the damaged hole(s) in place, and if the rest isn't too beat up it can be reused. the compression release isn't really needed, remove the residue & fly on.
if you can't fix the hole in place or there is other damage, the head will need to come off... that actually has advantages. it will let you clean things up & do a Stage I (or at least 1/2).... then it tempts you to 685/688 as well. think it over, all worth while mods
for sure I would pull off the left side engine cover(s) and look for damage to the cam drive train. I suspect the cams may have jumped time, check to see if that happened. if so, valves may be bent. I would seriously consider replacing the cam chain since it was stressed. might as well do the doo while you are in there... worth the piece of mind.