Fuel injector cleaner vs catalytic converter cleaner?

Hello, the ECT is the engine coolant temperature sensor, are you getting a code for the coolant temperature sensor along with a Catalytic Converter code? If there is a fault in the coolant temperature sensor or its circuit and it is sending the wrong engine temperature information to the engine computer, it can be enriching the air fuel mixture too much and that is what caused the Catalytic Converter to fail. Usually, cylinder misfires are what will cause a Converter to fail due to unburned fuel making its way into the Converter and the converter overheats and melts down. But a bad engine coolant temperature sensor will cause cylinder misfires as well because there is either too much or not enough fuel being sent into the cylinders.
The third diagram is the connector for the engine coolant temperature sensor and the wire coloring. Which is dark blue with a dark green stripe and the other wire is violet with an orange stripe.

You have oil leaking externally on the Catalytic Converter? That would not cause the converter to fail. Converters fail because of fuel getting into it internally and causing it to overheat. A bad Engine coolant temperature sensor could cause the engine computer to enrich the air/fuel mixture when it is not needed, this can cause cylinder misfires that will cause the Converter to fail. If you have a code for the coolant temperature sensor, replace the sensor with a good OEM (manufacturer) sensor, not a cheap one. And you can also check the wiring to the sensor, we can walk you through that. It's not difficult. But external oil leaks won't cause a P0420 or P0430. Cleaning the converter is not going to help if it has started to melt down, or it is not able to store oxygen anymore.
How did you trace an issue to the coolant temperature sensor?
With the coolant temperature sensor unplugged and key On, engine off you should read 5volts on the dark blue/dark green wire, the other wire (violet/orange) goes to the engine computer.

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

What code were you getting? P0420? And what parts have you replaced so far? The Catalytic converter gets to a very high temperature to burn off and convert any excessive emissions gases before leaving the tail pipe. I'm not sure where you live, but the outside ambient temperatures have been very high lately, so you might see the code come back at some point. Some codes need to have a certain number of faults occur and/or key cycles before a code is stored. Is your scan tool capable of reading live engine data? If it can, take a look at just the engine data while the engine is running. Look at the data PIDs for Long and Short Term Fuel Trim (LTFT, STFT). Those numbers will be either positive or negative, so for example +10% or -10%. If you see anything over 10%, that's when the computer is starting to compensate a bit too much for a problem, or what is thinks is a problem. If the code is not coming back right now, and you feel the vehicle is running pretty smooth, you don't notice any rough idle or lack of power, then check the Fuel trims, if your scan tool can't, see if AutoZone or another auto parts store will pull up that data for you. It will give you an idea of how the engine is performing right now. Quite a bit changes with the seasons, it takes more fuel to run a cold engine than it does a hot one, because of air density. So if you got the oil leak fixed, and its running okay, I wouldn't worry too much until the Check Engine light comes back on, but knowing the fuel trim numbers can help us see if the engine is on the more lean or rich running side of things, I think you'll find when that Catalytic converter code comes back, the fuel trim numbers will be negative more. And it's good that you always get a second opinion before changing out parts, many people will just keep changing out parts until something is fixed, but that gets very expensive fast.