I am aghast at the 48" center floor joists!!!!!!! 24" center floor joists are not legal---much less double that!!!!!!! If I were in your situation, I would add 2" by 6"s or 2" by 8"s between the existing joists to frame the bathroom area so you can install new a subfloor---I'd use pressure treated 3/4" plywood. Regular construction grade plywood would be fine also, but the PT would resist any future leakage better and once covered with flooring , pose no threat.(There is little threat anyway, but some folks feel differently.) Unfortunately, you will have to get into that crawl space---to install the joist hangers on the joists to either side of the one in the bathroom space, but by precutting them and having a bright light----as well as having the old flooring in the bath completely removed---you mighht be able to handle being in the space------you could go in through the bath floor opening which would allow you to set a couple of hangers and stand up---that kinda thing.

If it ain't broke and you don't need the latest style I'd just put it back. The valves and flappers fail in all toilets over time, there's no reason to replace the whole thing to repair those problems. If you needed to go to a lower flow, or had one of the '90's toilets that never actually worked that would be a different story. All that said, I'm very impressed with the new Toto's we put in our house. Not very expensive, work perfectly, refill quickly and quietly.

I’m not sure where your leak is coming from, I just wanted to tell our experience so you can gauge whether it might be a possibility in your case. One of our guest bathrooms had a leak that we originally assumed was from the shower. We hadn’t lived in the house for very long, and we hadn’t even used that shower yet when my sister came to visit. She stepped out of the shower and realized that water was squeezing up between the tiles when she stepped on them. Naturally, she informed us. My hubby had the entire bathroom completely gutted in half an hour! (It was a small bathroom with a Fiberglass shower, the tiles popped up like toast out of a toaster, and he’s just a beast... lol!) we see evidence of long term damage and provide my sister with another bathroom to use for the remainder of the visit. We didn’t start the bathroom remodel immediately, and when we did start it was slow going. We were very fortunate because we had barely started the remodel when we got another weather front move in with a whole lot of moisture... (It has been snowing a lot during her visit) and that’s when we realized the bathroom was leaking from another source! Hubby again ripped up the bathroom, and this time ripped out part of the wall that is on the exterior and that’s when we realized the leak was coming from outside. It took us a bit to figure out but we finally determined (with outside help) that it was because that wall was directly against an exterior chimney that had not been flashed properly. We left that bathroom unfinished for quite a while while we fixed the chimney problem, and waited for some more really good rain storms to make sure it was indeed dry before we finished our bathroom remodel. We were just fortunate that we have a lot of other bathrooms and this was just a guest bathroom. Anyways, I hope your issue isn’t something like that!

Mystery solved. (See my earlier post for the steps I had already taken to try to get a plumber under the house without success.) I scheduled two crawl space inspectors offering different services, thinking the joists under the bathroom would have to be replaced. The first one said that he didn't see anything serious under the bathroom, and the joist looks fine, but they saw some standing water under the kitchen. he said he wasn't sure if there was a problem or if there had just been some heavy rain. So then I was able to call a different plumber and say "we have standing water under the house." I feel what happened next is an example of exemplary service and professionalism. Even though the old copper pipes had been replaced about 15 years ago, there was a cast iron pipe has had corroded that only handled grey water. (It's not clear why this would have been replaced 15 years ago also, but anyway....) A team of two came out a few days later, did the work in the morning, provided photos and then one of the plumbers said... "We also were under the bathroom and saw that you have a leak from your toilet, so we are going to fix that for free to make sure the job is done right." (He showed me photos from under the house which were similar to the ones I originally posted.) Now all fixes have been made as far as I I know. We have a second crawl space person coming in next week and we're going to keep that appointment. The earlier estimate pointed to other kinds of work that could be done under the house - not sure if we need it, but since one raised the idea we want to match opinions to find out if we have any other problems under the house. Thank you for your responses, they helped me to keep looking and not give up.