The crux of all of this is that the UOA is more important than the VOA in gauging an oil's merit, particularly with the additive chemistry changes following API-SM.
I used Durablend for a time in the early '90s after it first came out. Never had a problem with it. In fact, this summer I discovered four leftover quarts of it, dated 1994. Gave it to a friend for his ancient K-wagon. He didn't have any problems with it, either.