A thousand thanks Richard!
Can't tell you how much I appreciate you being out there!!
You know I've been a carpenter/builder/plumber/handyman for quite a while...
And, I don't know if it's just me aging and growing in girth, the incredibly uncomfortable angle and way too tiny spaces for service access on an RV, or all of the above...
But I feel like the tail of
this bear is like that crazed bear that chases ambulances from this crazy movie my wife wants us to see... Whew!!
You've got the correct diagrams. (Mine is "VIEW E 64R") And you've circled the correct part on the
front view. On the back view, it's the
tee all the way to the left (circled in black) - instead of the elbow (circled in blue), on the right; which is the hot water supply for the outdoor shower. (The Fresh Water Inlet is circled in red)
See my photo below.
Here's a photo of my actual "wet bay" service area, with a green arrow pointing to the
problem child, aka "fill/diverter valve"
And thank you for thinking about alternatives. I always tell any so-called "master" builder/carpenter/plumber I meet... "I can never call myself a master - because I never cease to find a conundrum that I've never met - and "they" keep changing and making new things!" So as to say I always appreciate questioning. In this case - I am certain it is,
at least, the Fresh Water Valve tee.
It literally popped off and is shooting water out of the valve tee. Plus since I have been working on the area and
sticking, squeezing my paws behind the service panel I have noticed the threaded collar on the top end of the tee is cracked. (ALERT! ALERT! GREENHORN mistake not properly winterizing!

)
I have finally successfully removed all the attachment screws of the panel, and it is dangling by the plumbing. There is
some slack. And, it is probably possible (but as you said
NOT FUN) to work blind and replace the tee valve.
I guess that will be where I go after supper.
As an aside: I mainly wanted to fully remove the panel so that I could really get back there to inspect all the plumbing and for future maintenance. But since I am WAY pressed for time (we're supposed to be hitting the road on Friday) I'll settle for the tee getting replaced and hoping that does it for now.
Any further thoughts, ideas, humor, or prayers - are much appreciated and welcomed.
Thanks