BPF
In my own situation with the Seneca minus three rocker shafts and the resultant mess in the engine the unit would have very soon have failed completely. At that point in level flight the Seneca is happy on one. It was then more important to feather the prop and shut the unit down.
Whether that classifies as a partial failure I am not sure!
You only have to look at the failure rates between pistons and turbines to realize that complete failure is not quite ZERO
What starts as a partial failure can quickly deteriorate to a full failure.
You make an excellent and valid point that the majority of failures are pilot induced either through fuel mismanagement or engine mismanagement.
I am still amazed how many students are told not to touch the little red lever and how little is taught about correct leaning etc.
With so many bits flying around in a piston engine I am not as confident they are as bullet proof as you are
Pace