O ring oil resistance

["Bob Rochlin" <r_rochlin@hotmail.com>]

        Hi all,
        I just took apart the O/D inhibitor switch to repair it.  The
problem was the internal contacts were fouled with transmission fluid
because the O ring on the actuator has worn out.  If I can find a new O ring
does it have to be of a certain composition to resist transmission fluid or
will any O ring do?  Any help appreciated.  
Bob Rochlin
' 72 TR6