When it comes to tools I look for rusty or neglected OLD German,English,American,Australian or Swedish stuff because you can be SURE it was made to a standard and tested.Your cheesehead screws, by the way, will not be correct because they are made to a revised standard issued in 1958 (if you're lucky). The correct,and more rigorous standard which applied in 1946 was BS450 of 1932. Shape your screwdriver tip square and parallel for the full width of the slot.After many years of overtightening your threads may be a bit proud, so ease them flush with a countersink or dress carefully with a fine file.make sure you clean out the archaeological Red Hematite deposits from your holes and run through with a bottoming tap and paraffin.Prove the depth of all screws before fitting.You will then only need to exert even chimpanzee strength to obtain oil tightness, not the gorilla strength often employed.