A link to the rc10t3 (for some reason the b3 manual would not open for me) manual it will tell you how to fix the transmission.
You can clean the slipper pad with a scotch brite pad although it is best to just replace it. Also when you replace the pad replace the 5-40 lock nut (part # 6629) and the thrust bearing washer (#6594)
I like to clean the diff gear with Elmer’s sticky out it cuts through grease and does not hurt the gears and it does not irritate skin. Also WD40 is a great cleaner for the rest of the car.
When rebuilding the diff you should replace the thrust washers (part #6573) and balls (#6574), the diff rings (#9367) that is usually all but every 3 or so rebuilds replace the carbide diff balls (#6581), t-nut (#6575) and diff gear (#9365) also.