Images are not opening for me for very long - best I can see before the image disappears - it looks like you are referring to the boost valve. That increase pressure to the converter lockup piston. The metal plate on top should have a hole drilled in it if this is the area you are photographing. Has nothing to do with the gear changes or clutch failure.

The metal horseshoe that holds the boost valve in the valve body is prone to breakage.

Correction - the boost valve sees line pressure so depending on what is missing it may affect your line psi to the clutch stack.