I need help. My son has an older well used 12ga. Browning BPS pump that is malfunctioning. When the last shell is ejected the plunger & spring pop out. Is this because the plastic plunger is likely worn out or are the side rails worn out? is there any way to adjust anything to prevent this problem or just replace the parts. If it's a worn part where can I order the parts from and what part usually needs replacement? Any ideas guys based on experience with this problem with the BPS? Your thoughts please.