Waterlogged lower unit on 1960 Johnson 10HP (QD-21)

[silver_bay]

I was waiting for a part for another engine, I opened up the scrogged lower unit on the 1960 Johnson 10HP (QD-21) that came on my boat.

When I had opened the oil fill screw, the only thing that came out were a few dribbles of black water, and the prop was turning when I pulled the rope, so I went looking for an 18HP.

I got an impact driver yesterday, and opened the 10HP's lower unit. Other than a coating of brown muck, the only obviously broken part is the "shifter lever".
There was fishing line on the prop shaft, so maybe that compromised the seal?

Is the lower unit salvageable?

What steps should I take to clean/preserve the parts, even if I don't do the work now?

Max Wawrzyniak wrote to avoid post 1957 10HP's because of a weak lower unit; How do these lower units usually die?

Thanks!