Optimum performance of a cylindrical mirror analyzer (CMA) is dependent upon proper fringe field correction at both ends of the concentric cylinders. In many CMAs this fringe field correction is accomplished with concentric metal rings deposited on the surfaces of solid ceramics which completely seal off the ends of the analyzer. This paper describes the degradation in performance of the analyzer caused by the redeposition of sputtered secondary ions onto the surface of the conical ceramic at the input of the CMA. It will be shown that the time frame of this degradation varies widely from days to months (or even years) depending on the materials being analyzed and the mode of operation of the CMA. It will also be shown that the loss in integrity of the fringe field correction causes large changes in the energy transmission function of the analyzer. Errors in quantitative calculations based on the use of elemental sensitivity factors determined from standards run on a specific instrument at a fixed point in time can therefore be proportionately large. Alternate modes of operation which minimize degradation are presented along with a discussion of alternate fringe field correction schemes.