My family's had two of these one of these was my grandfather's from the farm. these thing are tough to kill, always ran straight 30, don't think it matters with loose tolerances just as long as it's a little heaver.
One thing about these, the oil drain plug is about 3 inches wide! That would make it very easy to investigate any crud on the bottom of the "pan". It also means that draining the oil takes about 3 seconds.
