[Kahuna]

We just did this on my friend's 52 Mercury.
Took the vacuum line from the engine to wiper, put that line into a glass jar half full of Brake Fluid. Have someone cycle the wipers back & forth, which will suck the brake fluid into the motor.
Let it sit over night, with a towel or something under the wiper motor as brake fluid wil hurt paint.
It'll probably work fine now. Did for my friend's