Please post a picture of the MPU with the wiring connected.

I was hoping to see much more of the MPU

You need to use the switch test, not the active switch test. With the switch test, you can uplug both connectors and short column pin to a row pin and test out to be sure sure each switch input on the MPU board is working.

The switch test should be the test right after the active switch test in the menu.

I never used a diode, just a jumper wire.

Do the switch test, it was made for troubleshooting problems much easier.

Install a new diode in its place and retest the switch test again. Just because you found one bad diode does not mean they are all bad.

What diode location was this one in?

If you have a DMM, it is much easier to do a diode test with it in the board. All the diodes in that section should measure about the same.

Nothing wrong with the 1N4002 diodes. You installed them in the correct direction?

And you are not using the active switch test for this testing, correct?

As I mentioned before, use the switch test, not the active switch test. It will be a lot easier to understand the problem better.

Any parts affected by the battery corrosion need to be replaced as it gets inside the parts. There is no cleaning will help the affected parts.

Need some good details when you short CN8 pins 1 to each of the CN10 pins 1 to 8, especially if the whole row registers a short, etc. You may be dealing with more than one row/column shorted so need to go through the whole switch matrix testing.

The corrosion seemed to have stayed away from the switch matrix circuit just looking at the picture straight down at the board.