All of the above but I have never tried Jims little trick. I have some tapered grinding tips that will remove the head of the screw as Ken mentioned instead of a drill bit. When I assemble an engine I use never seize on all the screws. Most people will tell you to use lock tite but even with the never seize I have never had any screws back out from vibration. For cutting a slot for a screw driver I use my dental hand piece with some very fine wheels but sometimes even those can't get into the area of the head to slot the tops. I use boiling water to heat the engines but the oven works just fine too. I have had to boil them then stick them in the freezer several times to get the screws out. The heat and shrink will loosen them up.