Tuning Crosman 1377 pump arm no longer locks into up position?

I gave my 1377 a good workout this weekend and after a few hundred pellets all fired with 8 to 10 and sometimes 12 pumps I noticed the pump arm (not sure what to call it) doesn't lock into place after pumping. I have to wrap a velcro strap around the barrel and pump arm to keep it from dropping. Any idea what's going on and what the fix is? I also put 50 pellets through the 1322 and the pump arm locks up after every pump. My 1377 has a Buck-Rail silencer on it, to put it on I had to remove the roll pin and stock barrel band and put the Buck-Rail barrel band which on because it has a threaded end to screw the silencer on and then put the roll pin back in. It worked perfectly until it started drooping this weekend. I probably need to tighten something up but have no idea where to start. The drooping forearm or foregrip doesn't affect function, but I know it shouldn't be drooping. Hope my question makes sense.