30-01-17, 10:46 PM
If that O-ring drops off on the way back through, or fails to seat properly in the oil pump, you could wind up with coolant leaking into the oil again and then you'd have a nice frothy mix of oil and coolant being circulated through all the major bearings in the motor. Like Dirty Harry said, 'are you feeling lucky?' 
Besides, you need to drop the sump to ensure that all the coolant in there right now is completely removed and everything nicely cleaned and dried before you refill with fresh oil.
Look the positive side, by the time you've put this right you'll have sorted out the header nuts and studs, probably given the EXUP a thorough service and you'll be much more familiar with the motor to boot.
Besides, you need to drop the sump to ensure that all the coolant in there right now is completely removed and everything nicely cleaned and dried before you refill with fresh oil.
Look the positive side, by the time you've put this right you'll have sorted out the header nuts and studs, probably given the EXUP a thorough service and you'll be much more familiar with the motor to boot.