SORTED !

On the BOB DIP switch 4 set on = "Relay 2 is turned ON"

On Ports and Pins "Output 2" = Port 1 Pin 17

On Spindle Setup "Disable Mist / Flood Relays" = UNCHECKED, M08 set to "Relay 2"

In hardware - abandon Relay 3 and use Relay 2 - this I think is the crucial bit as RELAY 3 IS A SPECIAL CASE !!!!!!!!

So now I can turn on with an M08 and Off with an M09 at will and can presumably also tweak the post processor to do as has been suggested. I think ALL my issues were caused as Relay 3 is a special case on this BOB

Very many thanks to those whose help and support got me here - much appreciated.