..well yes I could but one end of the lead goes into RX1 or RX2 and the other goes into either the P2Bus port or the M link port. Not much to photograph really.
I've repeated the update process and Terminal reported successful updates for both Rxs and the Mercury but with the same results. All still functions normally with M-Link. Since P2Bus is not crtitical for this application I'll continue on with M-Link and wait to see if the issues occurs with others.
Thanks for help