I'd try the nut splitter. Though you would need a relatively big one for this. Nut splitters are cheap, and even faster to use than "blue wrenches" (minimal setup). And they won't melt the rubber parts.
But first, make SURE you are turning only one of the nuts. There are two, stacked right against one another. The nuts will be a WHOLE LOT easier to turn if you take them one at a time. Perhaps you can use a backup wrench to separate them.
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