The aim of torqueing head bolts is to stretch the bolt within its elastic limits to provide a constant clamping pressure on the head gasket. This helps ensure a seal against combustion pressure and fluids. Some engines need a little help with bolt lube to ensure the take up is even and not in jumps to make the torques approach the manufacturers designed amount of bolt stretch.

I always clean the bolts with a soft wire brush and bottom tap the threads twice and blow them out between tappings.

Some Nissan manuals say to lube the bolts and most of the later ones dont.

The most common technique is now to torque up the bolts in two stages then loosen and retorque in two or three steps or angle torque them but mostly dry with no lube.

SR bolts especially sound like they are going to crack as they grab and release

I use a small amount of 20% 5 weight oil and 80% diesel on SR's to make them take up a bit smoother so you can get a more realistic torque reading.

I always retorque cold, after loosening back to 0 torque. Call me old fashioned.