Do not buy oil from O'Rielley's to add to your car, if you're running R12. They do not sell the appropriate oil. And don't ever add oil unless you think you need it. Too much oil is bad in a number of ways.

So there is still positive pressure in the system? How long has it been since it was serviced? A very small loss per year is acceptable, and almost unavoidable. Perhaps recharging it is actually in order.