Replaced the piston & nut assy for the GE GSD2800D03 with the replacement part WD24X10018 which GE indicates fits all 3 model subsets: D01, D02 & D03. Unfortunately the replacement part has a piston that is too short, it is 1 3/4" in length and the old piston in the D03 is 2 3/4" in length. Can someone provide the correct part number for this Piston & Nut Assy which is 2 3/4" in length. 
Blocked Washer Arm. The new piston by being an inch shorter does not seem to actuate the flap above it. ??
Yes I took another look at the parts breakdown and the shaft does look like it is extended in the drawing but there is no shaft showing in the actual picture.
Looks like this part has been updated and from your description the screen/flapper must also have something done to it but I do not know what that something is.
Hopefully someone else has actual experience with this problem.
Hopefully someone can advise where to obtain the original Piston assy. part 24x199 with a 2 3/4" piston length. That would solve this issue. All of the replacement piston assy. seem to have only 1 3/4" piston.