or a good harware supply should have the translucent plastic tubing. I'd replace the whole thing, rather than mess with a splice and have the old tubing break somewhere else. If your boat doesn't already have them, you can glue in the little nylon tubing routing eyes to thread the new tube through & hold it in place. If you can get the old metal fitting out, you can match a new one. Might be similar to a compression fitting for the plastic water feed line for your fridge icemaker. Don't know about your area, but I'm blessed with hardware & marine supply places here that have everything under the sun.
Paddler's Truck Rack