The valve body stiffener plate in the 2-3 accumulator area was eliminated on 2001-later 4R70W &4R75W transmissions. Oil pressure builds up in unused cavities under the separator plate causing the plate to flex upwards as much as .010", allowing forward and direct oil passages to cross leak. The Sonnax retainer plate 76507F-01K bolts in place and provides the clamping force to compress the lower valve body gasket. This prevents cross leaks, separator plate flexing and cracking, so that cracked separator plates can be reused.
Upon inspection, there are signs of poor compression in the underside area of the used gasket. Poor compression indicates probable forward and direct oil cross leaks.