A blown transformer at the Van Ness Muni Station in San Francisco caused the shutdown of the Metro subway system Monday evening. Muni officials said the transformer blew at about 6 p.m. as a result of rain damage from Sunday's storm. Subway service had not reopened late Monday, but light-rail vehicles were running on surface lines in the western part of the city. Also, cars on the F-Market line, which runs above ground, had been turned around at 11th Street for a time because of an earlier accident at Market and Dolores streets. The line was reopened at 8:35 p.m....