No need to pull alternator apart. Just remove rear metal cover (three 8mm hex nuts) and with battery disconnected remove two screws holding voltage regulator and bruxh set in place. Inspect length of two brushes. when new both brushes same length (about 1") but usually one wears faster than other so will be uneven.
I use a $20-25 replacement regulator Made in Brazil I get from my local alternator and starter repair shop.
As for your gauge reading differences between two cars they are probably just that different but OK. Proof is in testing with meter. I have one car that gauge reads high 15v and one that reads normal 13ish but both read about 13.7 - 14.5 when charging with multimeter tester.
I use a $20-25 replacement regulator Made in Brazil I get from my local alternator and starter repair shop.
As for your gauge reading differences between two cars they are probably just that different but OK. Proof is in testing with meter. I have one car that gauge reads high 15v and one that reads normal 13ish but both read about 13.7 - 14.5 when charging with multimeter tester.