It's a JIS screw head, not Philips. VERY easy to confuse. JIS screwdriver would have helped. Philips screwdrivers are designed to spin out of the screw head. A quality JIS screwdriver will stay in the screw head.

 

Hmm, widening the gap...
Why didn't I think of that?
I'll have to take a better look at the shaft when pulling off the shifter to widen the slot. I suspect that it'll be worn enough to warrant replacement.
It'll last longer next time around since I don't fall nearly as much as I used to.
Doh, just jinxed myself.

 

Thanks for teaching something new. I knew about Philips vs. PoziDriv, but never heard about JIS screw heads. Now I know why cross-head screws sometimes have a dot mark. My PH3 bit did fit pretty well into that screwhead, I couldn't feel any play, and did push on the torque wrench's head quite a lot to avoid cam-out. Now I wonder if it would be possible to find a JIS driver here in Thailand. Japan's not too far away and some Japanese cars and bikes are made here, makes sense if some tool shop had bits like this.

"JIS-spec cross-head screws are generally marked with a single raised dot or an "X". JIS always fit Phillip fasteners, but because of slight design differences, Phillips drivers may not fit JIS fasteners. (unless the tip is ground down a bit). "