Ask me, I know....
The nut is 18mm top and bottom, the top can be removed using a 5/8" slim wrench with the 18mm on the nut. On the bottom, the end joint is the bolt, so if you cut it, you have to replace the whole downlink. Try some vice-grips on the end joint and the 18mm gear wrench on the nut. Take some heat to it if it won't work loose but be careful not to destroy the rubber boot on the joint. PB Blaster is marginal on these nuts/bolts if they've never been taken loose.
I've broken 3 t-40 torxs, sears just keeps giving me new ones....