Following up for anyone who may be having the same issue with not being able to thread that part. I ordered a set of thread chasers which included M14x1.5 and M18x1.5, but neither of them were the same size so I believe that part is actually M16x1.5, but haven't confirmed this. As a last ditch...
Does anyone happen to know what size and pitch of the top bolt on the high pressure hose? It's the one with the 17mm head accessed from the top.
Tried to install new high pressure hoses this weekend but can't get that one part to thread. Anyone have any suggestions? Thanks in advance!