Comments based on over 27 years of using and selling AMSOIL:
AMSOIL does not cause sludge. Antifreeze in oil causes sludge. Excessive fuel contamination causes sludge. Some engines, because of the design, cause oils to sludge.
If AMSOIL caused a single engine to sludge, it is most likely that there would be another 5,000 to 15,000 engines sludged, since most of the engine oil is made in batches considerably larger than 5 qts.
I speak from some experience. My wife had to have my daughter's Saab when daughter moved to NY City.
Something to do with seats that moved up and down and back and forth by touching a button.
Car had had AMSOIL changed yearly (about 10K) since she bought it used with 60K on it.
Took it to shop with minor problem. Problem was fixed, and they replaced oil pressure sender unit since it was not working. Drove it home, and by the time I covered the 15 miles, got all kinds of bells and lights flashing. Yep, acute sludge.
Was it the oil? ****, no. First off, I have no idea if it had sludge when she bought it some 3 or 4 years ago. Unfortunately, the shop dropped the oil, so I couldn't get a sample for analysis-- I suspect some coolant contamination, but Saab has had some sludging problems (but mostly in newer cars). Should have had my 85 Saab (run on AMSOIL with 10K/yearly drains for the last 180,000 or so miles) fixed up, or told her to take a cab (which would have been much less expensive per year). Of course, neither approach would have been acceptable.