I was thinking maybe a crowfoot wrench but a Flex Flare might do the trick and it gives me an excuse to get a new tool!
I tried with an open-end wrench but you can't turn it enough without the wrench hitting the top of the motor. There is just no place else to go once the wrench hits the motor.
I just need to break the seal but not enough room with an open-end wrench. I'm sure once I break the seal the nut will be easy to back off by hand.