I am not familiar with that particular set up and have no idea how it functioned originally, but to have an encoder or eight position sensor and use an air motor, sounds like a basic design flaw, all the one's I have been involved with have either had hydraulic with hydraulic slow down before position, hydraulic servo, or at least air-over-oil.
To get an air operated device to stop on a dime is asking a lot IMO.
Al.