Radiator fan stuck on and on high in ignition and with engine running?

It may not be reading anything from the ECM side if its ignoring the fan or due to a communications fault. If the ECM is not able to communicate with part of the AC system or the other way around, many fans will default to high because of that. Other manufacturers do the same thing. If theres a loss of comms with the ECM and the vehicle still runs for whatever reason they default the fan to high to prevent over heating to the engine, when engine temperature cannot be monitored correctly. From what Ive seen that seems to be the case and its a logical answer, its better to have an engine run a little cooler than over heat so they just blast the fan on high all the time. But yes a computer for this Im sure is expensive. I would try a used fan first and see theres any difference. 100K to ground might be ok, considering its a signal wire. I dont think that wire is meant to carry current, it seems more like how a fuel pump module receives commands with a 12v duty cycle signal. Have you scoped the network to see if theres any distorted looking waveforms, everything should be pretty square with that Can bus, dont dismiss the network fault codes, what if you replace the ECM and still have the same issue, most places wont take a used module back.

You should be able to see on your scan data the engine temperature sensor change to an open circuit number, usually a temp sensor defaults to -40f degrees when unplugged, and you could back probe the ECM connector to see what the Bus looks like there.
Pin 1 green/white wire (CAN-C High) and pin 11 green wire (CAN-C Low) (twisted pair), if you have only a 2 channel scope you can go across those 2 pins and should see a bias voltage of 2.5volts, which is what the Can signal rides on. Can High should go from 2.5v to 3.5v and Can Low should be 2.5v down to 1.5v. Really youre looking for any weird sloping lines in the network signals, I like to take a first capture of a longer time base, that way I can see the very slight differences in each message packet, which is something you will notice. Each packet wont be exactly 3.5v up for example, but the slight differences are different modules communicating on the network. Its not easy by any means, I understand fully of not being 100% sure of what you might be looking at, I cant tell, just by a weird waveform, what the fault is, but when a square wave just doesnt look right you'll notice it, especially since youre a scope user which is really great. Not enough techs use them, I try to use for anything possible. If you have a good running vehicle around, take a look at its can bus so you can see what a good signal looks like. You can do a lot with just a 2 channel scope.
I was wondering if that signal changes at all with the ECM plugged in, does the scope capture have any change at all.

Hello, I thought you had this all sorted out already?

I assume you've cleared out all the codes after the last repair, what's the ECT getting to in the stop and go traffic (we'll call it city driving). It looks like 100c on the Cluster, so roughly 212f? Is that accurate to scan data? And are codes setting after 2 drive cycles?

These are the two coolant system diagrams, pretty complicated thermostat setup, Mode F shows coolant temp greater than 102c, thermostat fully opens to flow through the radiator. So that would be its max temperature unless I can find a different spec.

There are some pretty interesting info, along with the ton of other information on the cooling system, but I'm not sure what the water to antifreeze ratio is right now in the vehicle, but they have a very specific ratio spec and some reasoning behind it, if its 55% or more antifreeze, apparently this increases the boiling point of the mixture due to lower heat transfer of the coolant itself. So really it should be a 45% antifreeze ratio that will bring it to -22f freeze protection, But if there is a much higher ratio of antifreeze, which is difficult to tell unless its checked, who knows if the customer has just been dumping straight antifreeze in it over the years and the percentage is much higher now, you could check the concentration with one of those floating ball gauges, but it says to only use MB antifreeze as well. Not something that's well known I'll bet, about the boiling point changing according to the mixture. Regular people usually just dump in whatever is in their garage.

I'm not sure what color the MB coolant is, the green coolant is most likely just regular old antifreeze, but is the 100c temperature the highest it's getting on the gauge?

Well, 92c is only 197.6f, 97c is 206.6f, and on either coolant system diagram 102c is when the thermostat is fully opened and coolant is directed through the radiator, the 206f is okay with me, I know that a Subaru kicks on the cooling fan at exactly 204f because I used to work for them at a dealership. But remember that you did have a communications code from the Cluster to the ECM at one point, I'm not sure how much of the harness you have messed with since then, what's been unplugged and plugged back in, but I'm sure you would get a warning light on if the coolant temperature went too high. I know the temperature in Celsius can look foreign to us techs in the US, I usually just google a Celsius temperature to Fahrenheit, and it will bring up a conversion chart, it's just easier for me to see it that way as well.

I would drive it for a couple days and take a few longer drives to see if any codes are set, some take longer than others, but it looks like you're getting to the bottom of things finally with this vehicle.