A few opinions:

Castor: Although you can use medical grade castor, it is not quite as good for our purposes and it is a lot more expensive.

NORVEL engines: All of my .049's and .061's are Big Migs. The early ones said they would last 4-6 hours (CL), and "not less than 6 hours" (RC). I THINK this was assuming peak running with ~35% nitro. This was also the ABC version. The Revlites should last longer but in my Big Mig .049 Revlite instructions they have omitted the life expectancy. These engines are several years old so perhaps later they put it back in.

As someone mentioned above, how long it lasts often depends on how well you take care of it. Do you often run it on the lean side of peak? Do you use adequate type and amount of lube? Do you fly in dusty conditions?

Of course, some of us probably pamper them too much. I'm probably in that category.

George