Bicycle Mechanics - Play in road STI shifter

I recently bought a used pair of shimano 8 speed sti shifters, and the shifter for the rear has quite a lot of play in it, as in if I were to put it on a bike and ride it would move and rattle around over every little bump. I was curious if anyone would know of any remedy to fix this. Beyond removing the cover cap at the front (which cant solve anything) I really see no way of taking these things apart any furthur, and looking around with it open (as in the braking position) I cant really see anything I could possibly tighten.

Used STI shifters are a risky investment. STI shifters are nearly impossible to rebuild, a few people have done it. I doubt if you can find parts for an 8-speed shifters.
What part of the rear shifter has play?

Well if you were to picture it on the bars tightened down properly, the actual shifting + brake levers + the entire main body with all the guts in it can be moved from side to side.

Well if you were to picture it on the bars tightened down properly, the actual shifting + brake levers + the entire main body with all the guts in it can be moved from side to side.

The shifter "body" must be tightened with the rest of the package - do not attempt to disassemble the STI shifter in any other manner. If anyone has the instructions handy feel free to post them.

Ok, so I examined more closely and found the nut to tighten it, looks nothing like a nut, but i saw small grooves in it for a special shimano tool I figure, and it was hard to tell if what it was on was threaded or not, but I saw what could possibly be threads, so i used a small screw driver as a punch to tighten this weird nut down better and success!