GR-5 back to stock or to MM? Nothing has worked.

I have a GR-5 that I'd like to update to MM, but I can't get there. I was on stock Claro ROM (Latin America, Panama) but flashed an open ROM to get rid of some carrier crap. Everything still works, but now I'm stuck on this ROM because every full update.app I't tried has failed to install.

Can anyone help?

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