CJ -- DO NOT cut the retainer.. it will cause excessive pressure against the seal halves and premature wear.

Regarding the side seals, IF you only inject RTV silicone into those side vertical grooves, you need to add some kind of small wet (watered) felt strip into the side grooves.. because RTV .. with that type of thickness.. must have humidity to fully cure.

Otherwise, using the fiber strips often found in seal kits simply requires the strips to be pre-soaked in mineral spirits so that it will properly swell into the side groove.

Pre-molded rubber side strips may not fill the variable side seal gaps... the gaps vary per various production builds.