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KK1L said:

What I find most interesting about the detailed photos is how the corrosion is all on the exterior of the aluminum tubing. I would bet this has been discussed already somewhere. Why is this?

It is a night and day difference on the interior compared to the area trapped under the rubber hose. So which of these is the reason?
1) A reaction between the rubber, the aluminum, and the transfer fluid?
2) The trapped transfer fluid loses its anti-corrosion properties (changes alkalinity) over time and corrosion occurs at an accelerated rate? There is no exchange of fresh fluid in this area. It is stagnant. In the rest of the system there is a large volume of fluid which exchanges at least periodically.
3) Something else??

Is there some industry analysis of this effect? I would be surprised if there was not.

EDIT: It did not take too much searching to find this.
https://www.boydcorp.com/blog/avoiding-galvanic-corrosion.html

"In general, corrosion can be reduced through pH control and corrosion inhibitor use. The inhibitors attach to metal surfaces to passivate them and prevent corrosion. It is also important to maintain a stable water flow to avoid stagnant zones inside the cooling system, which can cause corrosion."

This sounds like it supports protecting the surface under the hose connection from exposure to transfer fluid, and changing the fluid occasionally.

Why is the corrosion only on the od of the aluminum under the EPDM hoses?

I haven't seen any definitive reason other than educated guesses.  My guess, it is in an area deprived of a continued supply of corrosion inhibitor in the glycol since it is a stagnant crevice that glycol seeps into but once the corrosion inhibitor is consumed, it is unprotected to corrosion.  This same method would suggest the glycol in the craves would become oxygen deprived also.  I read an article that states this area deprived of oxygen next to the oxygen rich glycol can lead to the pitting potential like we are seeing.

So which one is the reason?

I think it is your #2 which is what I described above also, but just a guess but apparently Alde has not given one.

That is a very good article you found and referenced, and your conclusion about coating the ends and glycol changes seems to be the best approach at this time in my mind. 

The glycol change every two year is the recommended practice along with the use of Rhomar glycol but recent information has shown a trailer with the Rhomar glycol change 2 years ago plus all new convectors and connectors had been found with corrosion on the inside of the aluminum pieces in the bottom of the glycol tank plus some pin holes in the new convectors. 

As soon as you think you understand what's going on, something else pops up.

OK, thank you we had tried that with no fix to the problem, but for some reason when we filled the freshwater tank and used the pump to run water through the faucets, all of a sudden it was working again. Not sure what happened or if I’ll have to deal with it in the future, but at least I’ve got working water for this trip. 😂 TY.