how can an a15 be great and an a12 not be, they are the same artitecture?

All aseries will last a great deal of time if serviced and looked after, i have had some unkown motors start up almost stright away from bening stored for years, and others that were used daily til a fe months before hand die straight away.

As with any 2nd hand part, its life span is unkown.

They all tend to have their niggles though, mine always seem to have leaky rear main seals (slight leaks), nothing major