How to check main site user level from subsite in a multisite network

The function current_user_can_for_blog() seems to be what you are looking for. With your example above, this solution should work:

 $blog_id = 1; //set the blog id to the main site id    
 if (current_user_can_for_blog($blog_id, "access_mainsite_s2member_level1")){ 
     the_content();
 }