Someone didn't RTFM did they?
Yeah, the screws were tightened with appropriate force at the time of mounting the reservoir.
However, as I wrote, I bumped it very slightly with my elbow when reaching inside the case subsequent to it's mounting. Contact was made with the upper most part of the reservoir thus creating a leaver effect multiplying the force of the slight bump my elbow made against it which apparently was enough to rip out the delicate acetal female thread at the base.
IF the female thread was a counter sunk brass insert of a slightly larger diameter into the acetal base, the endurance of the mounting mechanism would improve manifold which is why I think AC skimped on a relatively minor detail in an otherwise very high quality product.