Dear Yahi,
>Under load = engine exhibits intermittent misfiring<
Well the = intermittent missfire you speak of because of the Internal head leak is not similar to = the intermitant  violent  (emphasized) jerking of = the more mysterious problem related O2 sensors and AFMs that are = fixed with "harnesses".  I experienced this jerking once and = only once ever and never again,  acctually twice for a matter of = seconds on one day, who knows?
 
There is a great difference! 
 
 I do however have the internal head leak which I = believe has been worsening for the past few years.  A few mechanics = tried to find the problem to no avail.  I only realised the = acctual problem this summer on the way to maine to see Phish (there were = plenty of warning that this problem was happening, but I was young and = a newbie.) when my coolant light = started blinking,  the heater started blowing cold air = intermitantly for a while before the blinking.
So much exaust gas accumulated in the cooling system that the = sensor in the resevoir was responding to the fact that all that surrounded it = was air.  I pulled over and bled the system of air and topped = off the coolant (I was well prepared), and off we were again.  This = happened once again on the way home.
 
To make this increasingly longer story short.  It sounds to me like you = need to do the heads.  Feel lucky that you discovered the list.I did not find it 'till = last year and still took forever for me to find the real problem.
 
Who knows what other damage I have done by driving with = this persitant problem!  (feel free to comment on the possibilities, anyone?  she seems to = run fine other than the leak.)
 
One last comment:  Early on when I noticed slight hesitation on = take off, hills, ect.  I unplugged the oxygen sensor and this = remedeied the hesitation (not too smart).  I later plugged it back in = and it still ran fine but by this time the sensor was probly dead.
 
 
seth gordon 
84 = WLE