I would move along to voltage drop testing. For example with car running any voltage present between the centre of negative battery post and block? Centre of positive post and output of alternator. Resistance checking is not dynamic testing where under load voltage drops are.

There are some indications as well you could just be getting a string of bad rebuilds. I would not take a Mexican rebuilt unit home. They may have improved over the last few years though to be fair.

The logic being your original failure was an internal alternator mechanical situation causing the original alternator in you event to fail is almost beyond question. It was not external to the alternator in my opinion. So if we assume that this is true there may be no other issue there.

Believe it or not if the voltage drop tests under load especially on the negative loop where basically satisfactory. I would grab a used alternator from a pick and pull. You have to establish if your problem is really external to the alternator. My feeling is the junkyard unit would survive if you voltage drop tests where within reason. You really want clear of this headache by now. Test the used alternator before installation at one of the free testing places. You do not want to increase the variables in the process.

Sometimes I cannot see the trees for the forest either. Also get an old harness that plugs into your cigarette lighter for your voltmeter to keep a watch on the system voltages for awhile. These are just my thoughts, suspicions and what I might do if it where me.