When replacing the steering it is a good idea to replace it all.
On my jet I make sure there is a upward section that is higher than the water line so water only get so far anyway. It doesnt need to be far up, just over the water line at rest with a slight down angle to let water out. I also lube up the end with marine grade grease to help keep all the junk out. As far as I know the cable just rides in and out of the sleeve. No seal except where it goes thru the transom. ANd I think that is an O ring.