Murphy's Law is very evident in cpu cooling. It's one of the factors ppl consider a disadvantage in liquid cooling of any sort over an air cooler. With air cooling, there's only one point of failure from a device, the fan. With liquid cooling there's fan, pump, coolant, every connection. Now introduce peltier and that goes up again, power supply, connections, quality of contacts, quality of materials etc. With every possible point of failure being subject to Murphy's Law. And you want to Frankenstein an AIO/peltier loop, with a low flow, low pressure, non-distilled water coolant.
Cpu cooling is all about moderation. Especially of temps. I'd take a pc with constant 40-50°C temps from an oversized aio over a 20-30°C peltier all day. To the cpu, there's no difference. It works all the same under @ 70°C, no more effective or slower at 60° than at 30°. Which is where full custom loops shine. Moderation of temp, maintaining a constant, not extreme low.
Many are under the illusion that colder cpu is better, it's not. That's a byproduct of aircooling tech thinking where temps vary constantly from idle/ambient to load/extreme. So will bounce from 30° at idle to 60°+ under heavy loads, where cooling size and capacity are needed to cap the temp limits, and the more effective and efficient coolers like Noctua produces really can make a difference. Liquid doesn't work that way, especially not in custom loops. Liquids take a good long time to absorb enough heat energy to raise the coolant even 1°C, aircoolers being metal, take a second or less.
At 5 years old, that aio is suffering from only 1 condition, evaporation. There's been enough use/time that the chemical makeup of the coolant has broken down enough that oxygen molecules have bled through even the low evap tubing. Best solution (if you want to keep that aio) is to cut the tube, drain all the coolant, add distilled water/anti-fungal/anti-corrosion adative to top it off and a simple tubing splice to put it back together.
The addition of a peltier setup just raises any possibility of Murphy's Law application, which on that pc setup isn't warranted as ambient temps are not going beyond 40-45°C anyways.