[Turk]

You were advised correctly.
My MSD cap after only 300 miles or so, had things growing in it.
There was even some green colored foreign substance around the distributor shaft itself.
If I din't know any better, I would have guessed "moss".

I was told to drill a hole on the cap.

I did not believe t, so I called MSD tech support.Yup, that is exactly what they advised. They told me aproximately where to drill and how big and how many.
(2) holes across each other, 1/8" in diameter, close to the bottom rim of the cap. Preferably opposite of the retainer holes.

That is what MSD said..

TURK