In a situation that lays bare the difficulty of union solidarity even at a time of high public support for organized labor, journalists at the Pittsburgh Post-Gazette went on strike Tuesday — without the resounding support of their members. The Pittsburgh News Guild voted Monday 38-36 to strike, joining 50 of their colleagues — mailers, drivers, pressmen, and others — who had already been on strike since Oct. 6. Some journalists have refused to honor the strike and continue to work. Others have left the union in protest. The newspaper workers — from reporters to finance staffers to pressmen — …