Master Solenoid -corrosive fluid leak ???

Just back from Osh and I pulled the cowling to check things on my RV-7.
The master solenoid appears to have leaked corrosive fluid onto the firewall and further back on the belly. (no idea how to insert an image sorry). Have pics thou. Can send my email or PM maybe.
I first thought it was the battery, but the Odyssey battery looks fine.

Strange that the master solenoid seems to work fine.
What happened?
Obvious to replace the solenoid. But what is the fluid and how to best stop any corrosion? And how to assess the repair?

Has this occurred to others? I have never hear of this king of fail.
Other threads to search for?
Thanks much.

I am not aware of a master contactor that contains fluid.

Is the battery above the contactor?

Look again.

You had better go back and check the battery case for integrity. Corrosion did not come from magic. There is no other fluid down there that could corrode the stainless firewall.

Is there any deformation of the battery case, expanded? It would be an indication of overheating, maybe due to overcharging. This battery does not have much acid, but it is there. A tiny split in the case bond line could release a small about.

Kinda dumb of me to think the acid spill could be from the solenoids.
But I checked the Odyssey battery and I could find nothing wrong with the case. Really. But yes, the battery is above the solenoids. So I must admit stupidity, no explanation but from the battery.

So I start cleaning up the acid with a baking soda paste, and sure enough, there is acid bubbling out under the battery box. OK, solved.

I understand the acid spill from the Odyssey is most likely from the stock Nippon Denso alternator over volting. So I am considering options for the alternator. Upgrade from the $100 alt to a $400 alt with internal regulator, or go with an external regulator ???

I still don't understand where the acid came from? The Odyssey case was clean. Really.

Thanks for the comments.