You know, I just realized what the answer might be...
Thinking about the alternative question "If a gear tranny fails, what part of it fails?" lead me to the answer:
Something inside!
There is no real answer because each failure may be for a different reason.
Now a specific brand/model/type transmission may have a design weakness that shows up for that particular item, but it will not necessarily be shared by other designs or other manufacturer's products.
So...the generic answer to the generic question must be "Something inside..."
The points brought up referring to Ehydro systems indicate that perhaps a more general answer is needed:
So to cover all the bases we need to answer:
Something inside OR outside... /forums/images/graemlins/grin.gif
I don't think the initial question really has a specific answer. Just like a gear transmission could fail for any number of reasons, so could a hydro. Name all the parts, pick any one of them, and you have one possible reason...for a failure, sooner or later.
That is my take on it anyway... /forums/images/graemlins/smile.gif