How do hydraulic flat tappet lifters fail?

I used single springs with dampers, I have the spring rate and all the specs that I got from the machine shop at home. Okay, this go 'round I won't soak the lifters. I only used cam lube on the cam, assembly lube on everything else.

A friend suggested that running it hot will decrease the oil's viscosity and considering how it was the #1 cylinder that failed first, maybe that had something to do with it. His reasoning was that the #1 cylinder is farthest from the oil pump.