Hola Rafa, sorry but I've been busy.
I think the model you're referring on your M38 is the KSB Trico. To be fair I'm somewhere in the same position as you as the M37 that I used to drive 20-somethign years ago had the same, and here we are talking about the cinlindrically-shaped ones.
These are mine.
If you look at the unit on the left, there is a rounded knob (right next to the outer port) that acts as a pressure releaser. I think this is the way to activate it. Some other folks here that have the same model can bring some light.
The lines are routed same as in the Jeep, using the A-pillar of the windshield. I've never seen this model in action and I have them with me, not in the shop where the truck is (...yes, I know I should do test them).
Hoses can be purchased even in Amazon.
I'm still trying to know what this curved pipe does or what's the intention of having it.
A lot of people will tell to go for the electric wipers. More reliable, no problems when going uphill, less maintenance seems. Eventually I will, I guess.
From what I've read, Trico bought The Folberth Auto Specialty from Cleveland, OH a few years after this model came out and started commercializing it under the
Trico-Folberth name. The Folberth bros had the patent on the "automatic windshield cleaner" referring this model.
Small image, sorry (open it in a new tab and use the zoom).