Unreliable Perkins Range 4 starting

[PNM]

Both engines require 3-4 tries of the starter button to turn the engines. The engines start immediately once the starter is engaged and turning.

I have installed 2 new battery banks. #1 is 2 group 24 starting batteries in parallel with a combined 1600CCA. #2 is 2 golf cart deep discharge batteries in serial.

I have cleaned or replaced all ground and positive battery cables and cleaned all starter, solenoid and alternator connections. I have also cleaned all of the wiring connections on the starboard engine to include the starter button connections at the upper helm.

I have not cleaned up the starter buttons at the lower helm or for the port engine at the upper helm.

I shorted across the input and output connections on the solenoid on the port engine and got a very strong starter turning response.

I can hear a strong audible solenoid "click" when I press the starter buttons at the lower helm.

I did a min/max test while trying to start the port engine and got a minimum voltage of 12.72 volts.

So, I am about ready to rebuild both AC Delco Starters. I suspect the internal solenoid electrical contacts are bad or the brushes are gone on the starter.

But I am having a hard time believing both starters failed at the same time.

I will clean up all of the remaining wiring connections at the helms and try again, before rebuilding the starters.

You thoughts are appreciated.