The shutter times where checked/compared with long shutter speeds 1sec,2sec and 4sec which is easy to check against the same speeds on the F100. I pushed the shutter on both camera's simuntaneously and counted with a stopwatch for the secs. The F4s always closed the shutter first up to halve the speeds compared to the F100, underexposing in this way. So I'm sure the shutter's not ok in S(and in P?)
There's only the internal LCD in the viewfinder to check if speeds dailed in are corresponding, which I did: all speeds on the internal lcd correspond with the dailed in speeds on the top shutter speed wheel.