Re: Exhaust waterline question?
You're right to do check for water flow every time you start the engine. I suspect that the alarm comment was a bit of sarcasm. Most A4s don't have alarms installed, although they're a good idea as they'll also warn you about low oil pressure. The most common mistake I make when starting (always while sailing, not leaving the dock) is to leave the choke closed. After a few minutes I notice the engine is running very rough. It then takes a while to burn the fouling off once I open the choke. I need to install some kind of "choke alarm."
I noticed you said that your stuffing box leaks at idle. Is this all the time, even when the engine is off? If so, the packing nut probably needs to be tightened a little bit. The short version is, it should not leak when the shaft is not turning but should drip a little when the shaft is turning. If the packing nut is too loose, it will leak at idle. If it's too tight, it will overheat and the packing may be so tight that it scores the prop shaft, making it impossible to get a good seal in the future.
1977 C&C 30 Mk 1 hailing from Port Clinton, Ohio