No, absolutely not, never.

Lubrication system additives are never necessary as long as you are 
following the manufacturer's recommendation for oil change intervals.
Additives do not provide any protection or performance improvements,
and can in some cases cause engine damage or excessive engine wear.

The Federal Trade Commission <http://www.ftc.gov/> has settled with the 
makers of Slick 50 for making advertising claims that were "false and 
unsubstantiated."  Follow this link for more detailed information.

<http://www.ftc.gov/opa/1997/9707/slick.htm>