Note what the voltage "Set Point" is of the replacement voltage regulator module. My experience is common VRs are now running 14.8 volts which to me in our application is too high. I had to do some searching and came up with a 14.2 volt VR.

The Set point is the voltage the VR wants to see on the voltage sense wire (after the isolator). So you maybe seeing 15.5V at the center terminal of the isolator.

14.8V might be fine for quick recharging after start-up for personal car that just runs around town... starts drives for 5 ,miles then shut off. But our coaches typically run for several hours,fuel-up then run for several hours again. So 14.8V, or even 14.5V is high, so I went with 14.2V

My thoughts on diodes and regulator is if they are good old Delco parts, leave them alone. Replace the bearings and brushes, and clean all connections with D5 and reassemble. This has worked for me on GM vehicles.
And now a question for the experts. I understand the brush depressor tool (spray straw or wire provided) for reassembly, but is there a way to depress the brushes for disassembly so they don’t snap into the gap between the slip rings and crack the brush holder. Seems that happens about half the time for me.