you could go to any auto parts store and they will help you.
or you can go to
http://www.rockauto.com/ and plug in toyota/1989/celica (gt/gts or what ever)/engine/valve cover gasket.
BECK/ARNLEY Part # 0361479 is what you want. purdy much all online stores are like that.
comes with spark plug grommets.
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FYI, upon review of your history (Q's),
likely it's not the cause, or solution to your ruff running engine issues. when trouble shooting ruff engines, it's always best to start with a fresh complete tune up to get a good base line. otherwise, you'll be adjusting things to a false condition.
after your tune up, you might do a
http://www.seafoamsales.com/how-to-u...treatment.html treatment. if the issue still exists, take it to a shop for diagnosis.
or, you can go to
http://www.autozone.com/autozone/homePage.jsp .
it's a free online manual for your vehicle. has trouble shooting section as well. just sign up, plug in vehicle info, and go to "repair info".