Just bought a new G19 Gen4 this pass week. Owned several Glocks now & in the past. This one seems not to reassemble right. Just field strip it to clean it. The slide does not want to go straight back on like my other Glocks. It's as though the rear of the slide tries to ride uo off the rails and @ a angle. If I push down and muscle it to try & go straight back, it will. The slide racks okay, haven't fired it yet. Anyone else has/had this problem? Also noticed the copper color lube that comes new w/gun was almost entirely missing.