Can't solve P1093 - bank 2 too rich

[kevinkay]

Service eng light on/off for about a year. (mostly on)
Pre cat fuel trim too rich bank 2
(always only bank 2)
Seems to throw code quicker with highway driving

what I KNOW its NOT-
Definitely not the cat sensors -all new and thenreplaced and switched between banks
Not anything in the intake line - lots new and no leaks
injectors/plugs/coils switched between banks - still bank 2
Not crank case ventilation system
Idle control valve was cleaned (several times), rattles fine
Not the fuel filter/pressure regulator
not the MAF - BUT a new one kept the light off the longest
New bolts in the connection between the exhaust manifold/cat and the first muffler pipe (but I didn't replace the gasket).
I added an "O-ring" on the gas cap - its tight
compression test is good in all cylinders
Fuel tank breaker valve/purge valve replaced
new air filter
DISA "O-ring" replaced 45k miles ago - seals tight



big fear its the exhaust manifold gasket? -but no excessive noise
Changed my valve cover gasket about 60k miles ago, read it was the solution for someone else, but mine is showing no leak or smell on the outside, but could be one of the spark plug seals?

Anyone else have this code and got it corrected??
THANKS