Well, yep, even the manual transmission does seem to require Mercon. Ow.
If it's a 4WD, the diff and/or transfer case (can you tell I'm not really sure how the drivetrain's laid out?
) could still require gear oil... but if the actual transmission was full of it (and not blackened ATF), then unfortunately, it's probably worth a lawsuit if you can't convince them any other way.
Perhaps you can get your insurance company to do some of the legwork? I assume they could somehow be talked into paying for lab analysis of the fluid (to prove it's gear oil), since it's in their interest to discourage repair snafus that put drivers and vehicles at risk. In fact, getting a "you f***ed up!" letter from the insurance company might be more 'friendly' than immediately dragging it to court; I'd assume the loss of an insurance company's sanction would be a bit of a hurt for a small shop?
A small garage can easily go down to Advance or probably K-Mart and pick something "Mercon-compatible" up. (I think Dexron is effectively compatible, though warranty-voiding; it's Chrysler that uses fluid *completely* different from the other two.)
