1968 20hp johnson lower unit

[OTTERLAKE]

Question. I quit fishing and fired up the motor, gave it full thrust. went about 50 feet and thought the prop hit something and sheered the pin as it reved high but no thrust. Found out it was not the pin.still idles smooth revs up and down. must be something in lower unit snapped?? Any ideas on what may have happened. I dont know if it is contributing facor but the lower unit oil was a bit milky but not watery. when i put it in gear the prop can be spun freely with one finger in both forward and reverse.

Thanks

[OTTERLAKE]

found problem

problem was the drive shaft sheared off just above the pinion gear.