Your a bit in over your head.... He probably knows more about troubleshooting and modifying JV3 printers than most Mimaki engineers and pretty much anyone here on S101 so yeah - the Mimaki Doctor might be a good title for Alan.
And he is correct - have you tried swapping the data cables to that head to see if the problem moves to another head or stays with the same head. If it moves to the head you moved the cables to then it's not the head it's either the cable(s), slider board, main board, or possibly even the main cable bundle between the slider and mainboard. If the error 07 stays on that same head then the head is pretty much toast.