ask for kind help on J1 taxt

You would be appreciated greatly for your any kind reply to my questions:
1)Should I submit a 8843 or other any form to IRS for 2002? Now it is 2005, how can I do?
2)I heard the 2 taxes would be not paid within 2 years according to treaty article 19. Can I get social security and medicare tax of 2004 back?

The Situation is shown in the followings:
I once came US as a visting researcher for a short term within 2002 (less than 3 months) and not got any pay from US. I did not submit any forms to IRS because I did not know anything of tax.

At the second season of 2003, I arrived at US as a visiting researcher again but got wages from university. No social security and Medicare tax, of course no federal and state tax. I submitted a 1040NR-EZ to IRS.

At 2004, I was treated as RA, I paid social security and Medicare tax while no federal and state tax.