water fixture on tub

I found that my water fixture on the tub has a leak right where the shower hose connects. What has to be done to replace the water fixture on the tub? I have replaced many on the sinks in the house, but none in a camper. I have a 2002 2720SL.

I originally thought the leak was at the shower hose connector, but it's actually right below that connector on the water fixture side of the threads.

Thanks.