My shifter is nuts!

http://www.google.com/products/cata...a=X&ei=w91HTs2NE9HRiAKkzK3wAQ&ved=0CEYQ8gIwBg

or

http://www.google.com/products/cata...TpWKFc7YiALw_K3LAQ&ved=0CFwQ8wIwAA#ps-sellers

Get the threads totally clean before you apply. Should solve your problem.
Available at any auto-parts store.