From memory, one is tricky to reach, but I solved that by using a small Torx bit and turned it using a small adjustable spanner while maybe applying a bit of pressure - to keep the bit fully down into the head of the screw, by forcing a small flat head screwdriver down on the outer end of that Torx bit.
I thought that I'd be clever and ordered in a pair of galvanised back plates via Autodoc, maybe along with some other parts, they are good quality, but I felt the urge to spray them with black satin Hammerite, now okay that meant that they looked OEM, but it seems that whenever I wash the car and reach in with a long wheel brush to clean the "barrel" of the wheels, I keep knocking off or removing some of that black paint.
The "rusting in" will only be the actual exposed heads of the screws to the outer face of the splash guards, there should not be any rusting on the shank of screws as all these holes are blind holes.
Edit:- sorry for the delay in spotting this thread.
