INSPECTION: As you did with the housing, you will most likely see minor circular scratches in the cover plate's hardened surface. Unless deeply gouged, most of these wear marks or machining imperfections can be satisfactorily smoothed over and polished to a glass like slippery surface.
SMOOTHENING: Take a 8x11" sheet of coarse grit emery paper in 80 or 100 grit place it on a known smooth surface such as a marble counter top. Lay the cover plate with the gear side surface down on the emery paper and begin evenly sanding the surface being sure to move the cover around the paper and not just in a single back and forth motion. The goal here is to smooth out the scratches and grooves, but not necessarily remove the ones that are too deep. Since the cover plate's thickness will not affect the gear rotor and housing clearance, you can remove more material of you need to in order to smoothen the cover surface.
Once the internal surface is satisfactorily sanded, move up to 240 grit emery paper and perform the same procedure as above. The 80 grit removed some minute material while the 240 removes the scratches left by the 80 grit. One that is completed, you can use a finer grit sheet of paper with a dab of oil to make the surface smoother and smoother before the final buff.
POLISHING: Once you have completed the sanding procedure your use a bench grinder mounted buffing wheel to further smooth the surface of the rotor side of the cover plate. First use Tripoli rouge compound for a coarser smoothening, then use the softer White rouge for the final buff to a high lustre. Remember once again to buff all the surfaces evenly and uniformly. Buffing compound can remove additional metal as did the sanding operating, so care must be taken not to concentrate only in one area instead of evenly across the entire surface.
The illustrations to the right show the high lustre that can be achieved and the incredible amount of smoothness that is able to be achieved. While only the deepest grooves may still remain, there is a significant reduction in oil leakage potential across the previously numerous scratches and a dramatic improvement in friction reduction and cooling benefits as a result.
FINISHED PRODUCT: The photo to the right clearly shows how smooth and slippery the surface now is and most of the scratches and grooves are removed and the one or two that remains are fairly insignificant and will not adversely affect the pump's sealing characteristics.