A generic "Ford" solenoid will work fine as a replacement. Some have two
small posts. One is to activate the solenoid the other is an output to
bypass an ignition resistor. If the solenoid you get has two small posts,
just put the small wire on one post, if it does not activate the solenoid,
just move it to the other post. It will not harm anything doing this.

A new water pump impeller would be a good idea.

If the lower unit oil is milky, remove the prop and look for fish line
wrapped around the prop shaft and holding the prop shaft seal open or maybe
even doing damage to the shaft seal. If the oil is milky, replace it with
fresh lower unit oil. Check it often to find out if you have a seal
problem.

Don Dando