Rainsoft valve problem

I have had a Rainsoft water softer for about 6 years now, the valve has the model#AQ24CT on it, it is a touchpad electronic unit. The problem I am experiencing is the plunger (correct term?) the is driven by the cams and changes the direction of the water through the filter has 3 o-rings on the column. Every year I have a problem with o-rings coming out of their grooves and jamming the valve. Is there a replacement available for this? You would think there would be a plunger with permanent gaskets instead of o-rings that can become dislodged. HELP