Need Some Expert Advice Please, Anoluge Stick replacement Not working

I've just replaced the analogue stick with a brand new one. Ike replaced one before all i did was unscrew the psp unscrew the old analogue stick and put another in the same place were i took the old one out off. so i thought it would be as simple as that this time..

This time i just replaced a new one and did like last time just screwed in the new one and put it all back together. Didnt work this time still keeps doing the same thing if its a game were its a language selector it will just automatically starts scrolling through them very fast! so i thought maybe it was a faulty anologue stick. so i got a new one. I havent put this one in yet to test it, but what i did notice was in the packet the anologue stick came in there was a very small rectangle thing! now maybe thats the piece im supposed to put in with it, the problem is i have no idea were im supposed to put this little rubber thing as ive never noticed one before, if someone could maybe help me a little id be forever greatly in your debt. even a pictured guide were someone could point me to, explain were it goes. Not sure if its if any use but i have a psp phat and its the psp phat 3d anologue stick i bought to fit in it i just dont know were this rubber thing goes or why its not working.

Thanks ever so much for taking your time out to read all this, im very greatful indeed and hopefully one of you experts out there could shed some light or point me to a nice simple guide.

Thanks Again
2fast2C

Please excuse my spelling!!!