Dear Jayson;
DOT (Dept. of Transportation)3 is the specification that was used for many years until disc brakes came to be in the late 60's.
Due to heat generated in these systems (disc)the DOT raised the standard.
The hole you mention is a vent for the master cylinder & necessary. Also; brake lines don't 'rot' as they are stainless steel and the rubber ones are a special material especially for hydraulic use(s) due to the movement of suspention/stearing parts.
If a brake pedal is 'spongey' there is probably air in the lines.
Good luck, John M......
