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The original flaw with OEM sunroof seems to me that the cover is very good at sealing the small compartment away from the rest of the car, and the portion exposed to atmosphere on top is also small. So water vapor gets trapped between the two spaces and especially when sun hits it- high energy/velocity water molecules and oxygen attack the delicate intricate metal mechanisms contained within this space (it rusts the metal parts at high rate) such that twenty years later every single 240 sunroof with a cover is rusted badly.
The trick of course upon ownership is to immediately restore the surface by sanding/wirebrushing back to mostly plain metal and rust transition state and then painting/coating with some kinda permanent rust inhibitor designed for that state of metal (like a POR-15 which hasn't let me down yet. It doesn't come off of skin or clothing btw...) and then leave the cover open 1/2" or so. That tiny little gap allows the water from above to escape into the car which keeps the water from attacking the metal up there. Which of course if you have alot of it (many days of rain constantly I guess) could be an issue (Solution B: damprid desiccant exchanges) but this all assumes the mechanism survived intact enough to be operational in the first place.
The gap also keeps water from pooling on the inside glass. It just has nowhere to go when the cover is shut tight. Ironic since that is what the cover is designed to do- working as intended.
I Wonder if a spritz of WD40 wouldn't have prevented all of this, once per year or something by the original owners. If they were aware of the issue... how many perfect sunroofs would still be here now. I guess the WD is an ideal solvent/rust inhibitor for the mechanism because it is quite comfortable with water while still functioning as a lubricant. A rare quality for an oil but important in systems like this where we can't just raise temperature to 212*F all the time to drive out water (like engine oil).
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