Years ago I butchered one of those wretched screws and ended up drilling the mongrel out, damaging the nylon surrounding the screw in the process. I since found out the screws are JIS type meaning a Phillips head screw driver will quite possibly damage a difficult-to-move JIS screw. When I put the cruise control in Rubina recently, I used an "OZSTOC JIS" driver- that is, a #2 Phillips driver with 1mm of the tip ground off. I also gave each of the 8 screws a mild tap (on the top of the screw driver) which helped to get them to budge.
You should use a JIS driver on all the ST's screws- the grip feels really positive, unlike a Phillips driver.