Fresh oil in coolant... Crack in bore?

Hey guys.
Here goes the story.
Had wagon in for major service and timing belt. Found oil in coolant. All tests done. Had radiator out and tested. No faults found in any of the pressure testing. But clean oil keeps coming through in to the coolant.
Mechanic says that in his opinion it has to be a slight crack in bore that only happens under operating pressure and temps. How does this sound with everyone who has gone down this similar path of problems?
I'm currently putting together a list of upgrades for when/if we need to take motor out. Any advice in this area would be much appreciated too =) keep in mind that I'll be going to E85 at the same time!
Here goes the story.
Had wagon in for major service and timing belt. Found oil in coolant. All tests done. Had radiator out and tested. No faults found in any of the pressure testing. But clean oil keeps coming through in to the coolant.
Mechanic says that in his opinion it has to be a slight crack in bore that only happens under operating pressure and temps. How does this sound with everyone who has gone down this similar path of problems?
I'm currently putting together a list of upgrades for when/if we need to take motor out. Any advice in this area would be much appreciated too =) keep in mind that I'll be going to E85 at the same time!