i just picked up a Glock 21-SF. i havent shot it yet. initial impression are great. one issue is the slide release button. i have a past thumb injury (table-saw) that left me weaker and slightly numb. i know i will have issues releasing the slide. it is much burly-er than my other pistols. i googled it and found an extended slide release option. is this a factory option/upgrade? or is this an aftermarket part? will it even help me? tell me what you know, please. cliff.