We were off on our summer cruise preparing to haul anchor. The engine had been running fine the day before but it refused to start that morning. After checking and replacing the fuel filters and cracking all the bleeder screws I tried the WD-40 trick. It fired and ran fine. After consulting with a marine mechanic I learned that the M4-30 is a notoriously cold blooded engine which needs the glow plugs for the first start of the day. Long story short, it was a failed solenoid which controlled current to the glow plugs. It's likely a problem unique to that model Universal engine but worth checking.