The Sr. Swing control box has the power boost feature which the Mid Swing control box did not have. If you replace only the Mid Swing control box with the Sr. Swing control, and the power boost ever gets turned on, the Mid Swing gearbox will run backwards, indefinitely. When replacing an obsolete Mid Swing control, you will need to replace BOTH the Mid Swing control box and gearbox at the same time to the Sr. Swing parts.
A Sr. Swing gearbox will work in a Mid Swing operator. However, the Mid Swing will now have an opening force of 11 lbs. (approximately) compared to 8.5 lbs of opening force of the Mid Swing gearbox.
A Mid Swing control or gearbox WILL NOT work with an (obsolete) Astro Swing operator.