Pulled the dishwasher out of the cabinets. Took photos of the incredible mess behind it. Cleaned up the mess. Went to Home Depot. Bought screws for the racks, and a roll of galvanized flashing and some metal-to-wood screws, and a cap for the hot water line where the dishwasher was connected to it (single-valve y-joint, so the sink has no hot water when the valve is closed). The screws for the rack work on one rack but not the other, unsurprisingly. Went back to Home Depot and bought different screws. They don't fit either (right size, but wrong threadcount). Checked the internet, sure enough, shoulda done that first. #12-24 for the telco rack, #10-32 for the audio equipment rack. Went back to Home Depot AGAIN, and they were closed. Came home. Cut the flashing to fit. Bent it to fit. loree chiseled out the sprayfoam from where it went. Installed the flashing. Stuffed some steel wool into the gap left over. Took a shower. If the house does anything further to me today, I will burn it down.
Will add some copper mesh plus sprayfoam and more flashing tomorrow, after going to Home Depot for copper mesh. Apparently, steel wool isn't a big deal to rodents. They get used to it and chew right through. Copper, on the other hand, they can't stand.