I inherited a Winchester model 1400 semi auto shotgun. When I fire it the fore-end gets shoved way forward. The serial number is 7xxxxx. I have seen parts diagrams showing fore-end spacers. This shotgun has nothing under the valve cap. The spacers are shown for serial numbers below 400000. I need to know if I am missing parts or if the fore-end is just worn out. I can replace it with a composite, but I like the wood. Any info would be greatly appreciated.