84 F250 Diesel with a C6, I had a servo gasket start to leak, so I got a new gasket and seal and took the old ones out. I found a strange hole machined in the housing, next to the lower rear bolt, it does not match the servo, but appears to be there for a reason. Wondering if a previous rebuilder has installed the wrong servo.
The housing has a bit of a web, in that area, which looks to have been designed for an additional passage, I cannot confirm if a passage exists, none of my other C6s have this. I have not yet been able to confirm if any C6 servos or gaskets differ in this way, any old school C6 guys ever heard of this?
This hole undermines the gasket, and that is where my leak came from.

 

I figured it out, other year shop manuals show that hole, and one even shows the ridges on the inside, but they show the same basic servo as mine, which does not cover the hole. I guess I was just over thinking it, I will re-install what I have.
I have C6s from 70, 77, 78, 79x2 &80 without that hole, but when I got home, I checked my 66 Lincoln C6, and it has it, with a normal looking servo, so I guess the hole was just left half open on some, for some reason.