Lexmark P3120 PrinTrio error

I replaced an ink cartridge in my Lexmark P3120 PrinTrio and when I closed the printer door I heard a pop! Now I get the msg printer door open.

I know what has happened, there is a 1 inch long plastic rocker that popped off in side. It feel out when I was examining the unit. It doesn't appear to be damaged, it looks as if it just snaps back on. But the problem is. How do you open this printer up?

I went to Best Buy where I bought it in Feb. of 2004 and they won't even send it in for service. It prints really well and I don't want to drop another $150 on a new printer, because of a 5 cent part.

I need to know how do you get into this printer. So does anyone have a sevice manual?