Of course you woun't magnetize a G17, that's one of those plastic guns. :grinThat's been laid to rest personally. I bought a magnetic belt holster from a street vendor trying to get me to carry that line. The question came up about the gun parts becoming magnetized and affecting operation in some way.
Left the trainer g17 on the magnet holster for several months. The gun nor parts were magnetized in that time. The gun hadn't suffered any maladies being discussed here.