Does it leak only when the wh is on? I just had my "working just fine thank you" wh serviced at CW and the first time I used it, it leaked at the wh but only after the unit had time to heat up. The leak was not at the water inlet/outlet connections or anywhere down stream. It's back at CW for them to find out what happened.
On your second question, I replaced the shower faucet in my shower and it was a piece of cake, but your much newer model may be more complicated.
2016 Newmar Bay Star Sport 3004