Here are a couple more tricks for knackered Phillips screws. Of course none of these will work every time and some are not appropriate for every application.

1. Use a Dremel with a cut-off wheel to cut a slot in the screw and then use a regular slotted screwdriver. Grind the screwdriver tip to exactly fit the slot you just cut. Yeah you have to sacrifice a screwdriver. Small price to pay.

2. Use an impact driver. Get a cheep one from Harbor Freight. They work terrific. You can also use the impact driver for trick #1, above.

3. Take a flat-headed punch and carefully use it with a hammer to 'hammer down' the distorted Phillips X to re-form it back into shape. THis only works so-so.

4. Use a chisel or Dremel to cut the head off flush and use a left-handed drill bit to drill the screw. This will usually remove the screw outright.

Use the impact driver combined with the valve compound and reforming the Phillips slots and I guarantee you the screw will come out.

These are all stock-in-trade for anyone who has ever worked on an old Japanese motorcycle...