On our 2015 28FC, we had a leak around the shower and I pulled the access plate off the back of the shower to examine. Turned on the water and all looked fine around the valve. However, when you would press the button on the shower handle to get a stream of water, it leaked tremendously from the connection behind the shower. Easy fix in that the mothership had used a too thick of shim and the connection didn't seal completely. On yours, it could be the connection just loosened up over time from use. Simple to tighten and no more leak. On ours, I put a thinner shim in and it then mated well. No more leak. Only occurs when actual shower handle is turned on. Just having water on in shower it will not leak.
Don't know if that's your issue, but might be a starting place.