I have tried adding the recommended 3 pints and that doesn't always seem to work as well the good ol' dipstick I have in mine. The original drawing for the model 20000 (print #M-20001) I have from 1971 calls for 3 pints. Line item #16.
Can you see through your sight glass? It might take a flashlight and a mirror. If not I can take a measurement from my dipstick and you can transfer it to something of similar length. A chopstick works well.