Northampton could be facing a multimillion-dollar decision over its deteriorating downtown parking garage. Engineers say the E.J. Gare Garage has extensive structural damage and recommend demolition rather than repairs. Replacing it could cost as much as 33 million dollars. More than half its parking spaces are already closed, and the city is spending about nine thousand dollars a month on temporary supports. Mayor Gina-Louise Sciarra says officials are exploring alternatives, including a smaller surface parking lot.