Cylinder head gasket/gaskets should not be re used again when pulled from powerhead, will be found compressed, hardened or overheated. Always install new ones for a perfect mating surfaces seal.
With respect to slightly grease general bolts one thing is putting huge mounts of grease on bolt's threads other putting very little portion on a clean or new bolt.
According to my experience tearing powerheads down to clean all water paths as when out of the box, when lightly greasing bolts have found very little torque difference due to grease rather by not re torquing head bolts back again when out of the box.
Bear in mind that OB's powerhead gaskets needs to be re torqued to factory specs soon after break end period has ended or soon after which must be done by dealer or qualified mechanic, gaskets will be somewhat compressed due to combustion heat and needs to work and seal again where once were torqued to when new or replaced, very few boaters, assume none performs a re torque work, that's with a high quality torque wrench not by hand.
To light grease a bolt, simply get a small round brush, dip it in triple guard grease and draw a fine grease line right in middle bolt, put it back in on cylinder head and torque bolt to specs and don't forget to re torque gasket back to specs soon after first 10-15 worked hour use if wanting OB to last for years to come in excellent shape.
Happy Boating
