Copper fails due to freezing, corrosion, or movement fatigue. To some extent you can control all these by using the right solder, cleaning off flux, insulating, strapping pipes properly at stub-outs, accommodating thermal expansion, damping water hammer, etc.

Most houses in the US are expected to be replaced after 70-100 years of use. And all in-wall utilities have a finite lifespan. So the critical question is how often they need to be replaced, and how much damage occurs during a failure. In my experience/opinion soldered copper is proven good for 50-100 years typical between repipes, and PEX is probably good for 30-50 years between repipes. Accelerated-aging studies using high temps show it should hold up better than older stuff like orangeburg or CPVC that have clear reliability problems. Unfortunately, modern connections like propress and sharkbite don’t truthfully have enough field service history to know if they’re 20 year fittings or 50 year fittings or 100 year fittings.

If the refill hose is stuck down the overflow tube too far, it will continuously siphon a trickle of water into the bowl.

Something to remember with caulk is that you need a certain bead width to accommodate a certain amount of movement. Wood expands and contracts seasonally. A 1mm wide bead of caulk would need to stretch 100% to stay intact if the 1mm gap becomes 2mm in winter when the wood dries out. Most caulks can’t do that, and will crack. A 3mm or 1/8” wide bead of caulk is more likely to be able to stretch by 1mm up to 4mm without breaking. So in a serious way, caulk is better at filling BIG gaps, and a poor solution when the fit is quite close. Check the expansion rating for the product, and think about how that relates to the movement of the gap you’re trying to fill.