I have a TM M4A1 that i recently bought from ebay...(i know...i know) and pretty much the only issue with it is the charging handle spring. I can get a spring easy enough, but what does it attach to in the upper reciever? It looks like there is a place where a pin is missing right above the hop up, but i'm not sure. Any help/advise woud be great. Thanks!

there is either a screw that goes into the upper reciver, or a little plastic hook looking thing that that is up in there that the spring slips over. not on the hopup though.

Yea i assumed the same thing, but there isn't anything there. There are two ridges on either side of the top of the reciever that looks like some little pin should sit in there, but i wasn't sure so i was asking. I'll try emailing the guy i purchased it from, see what he says. Thanks~!