Is this a 90+ (high efficiency) furnace?

In general, it's best to remove as much damaged wood as possible, and replace it with a paste EPOXY, like PC-Woody (strong, wood-colored), or PC-7 (very strong, but gray), or PC-Concrete or Simpson Strong-Tie ET/SET anchoring epoxy (KILLER strong!... but concrete gray color). Beware of Bondo and similar auto body fillers. They are made to be sealed with paint, and will soak up a LOT of water if they are left unpainted. A bleach solution WILL kill everything IT CAN GET TO in wood, but TSP (tri-sodium phosphate) will enhance the process by making the solution "wetter", and thus able to penetrate deeper, and GET TO more rot. Most brands of TSP will have recommended proportions of water, bleach, and TSP on the box. TSP is sometimes marketed as "Deck Cleaner" in order to boost the price of this simple chemical. As for the Minwax wood hardener, it might be OK, in some apps, but it's pretty lame compared to the LOW-VISCOSITY EPOXY RESINS designed for the task of soaking into wood, consolidating the loose stuff, and then curing into... epoxy. ;') There's "PC Rot-Terminator" from PC Products, available on Amazon.com, and "RotFix" from System Three, available at Woodcraft stores. It's not cheap. With any epoxy product, THOROUGH mixing of the 2 parts is essential to success. Here is a link that might be useful: Some useful info/video on rot and products...

We just finished covering the vinyl asbestos tile in our basement with the click type flooring and I am pleased with the results. I was sure that the original floors contained some asbestos because the previous owners left an original carton behind. In our laundry room, I wasn't sure about the asbestos content so I sent samples to a testing lab to find out, and the cost was reasonable. I recommend doing the testing so you know what you have before you cover it up, partly because you might have more options if asbestos isn't there and partly because when you go to sell your house you can address the asbestos question definitively. We used a Cortec product that is supposed to be waterproof, and I am happy with it although it has taken me a while to get used to the odd kind of hollow feeling the floor gives me, compared to walking on other floor surfaces.

Cat_ky, I will probably do that eventually. I don't know how they'll look into this other than cutting into the ceiling below--unless they can see what they need to see by removing that gasket. I just did some measuring, and it actually looks like my shower straddles my laundry room and garage. The drain is probably right above a wall. I might try asking my neighbors via Nextdoor if their drains appear the same. The part that really concerns me is the top of the pipe and how it's raised above the gasket and the edges are rough--doesn't look like the water will all drain out properly and will instead sit on top of the o'ring.