Some go so far as to describe this practice of crimping shut the overflow line as 'a used car lot trick':
H.A.M.B.I guess I would like to hear more about logic behind this 'field' engineering change.
After all the purpose of the line is to provide a certain rate of flow up top. Crimping the overflow restricts the flow rate through the line which in turn will likely promote deposits in the line itself - further reducing the volume of oil reaching the rocker shaft.
Keeping the assembly clean (as the shop manual describes) seems the best plan. Making sure that the overflow is properly directed to the drain hole will prevent excess oil from collecting on the head.
This is the design intention (as I understand it).
