Originally Posted by Air&Road

If you're talking about the screw on the clamp for the prefilter hose, just cut the clamp and buy a new one, or both of them.

Hope this helps.

Whoops.... scratch that. I just came from the diesel discussion and had 240D on the brain when I wrote the above answer.

You might try cutting a slot across it with a Dremel tool and a cut off wheel. Then use a flat blade on it.

A trick for next time you deal with a stubborn phillips screw: mix up a paste of water and scouring powder. Make the paste with very little water, just enough to make it as thick as mayonaise. Then stick the philips screwdriver in the paste and then use it on the screw. It works great for gripping the screw.