I'm fairly sure the shaft I'm playing with won't go anywhere, but who knows?
The level you describe in the Ogof is blind if it's the one I'm thinking of. However, many years ago, a dig was conducted right under the ventilation shaft and showed it continuing downwards. The theory is, that the shaft was sunk in more recent times and connected with the lost Llanymynech Mine. There is a survey of this mine in Oswestry library, and if you take a compass bearing off it, you'll come to a strange, mud filled and blanked off feature halfway down the quarry. Possibly, most of Llanymynech mine was quarried away in the C19?