I aligned the Xgreen and PSL green to overlap on the X beat PD, and reconnected the splitter which combines the X and Y beat signals and sends them to the control room.
I've been stepping the Xend laser temperature offset in steps of 20 counts, making sure the cavity unlocks and relocks on TEM00. So far I have not seen any beat signals for the Xarm. I've gone from 0 to 840.
I'll be back in a few hours to keep trying, although interested parties are invited to give it a whirl.