The left seat adjustment rail for the driver's seat cracked all the way across immediately behind the bolt holding the forward end of the rail to the floor. this allowed the drivers seat to rock back and to the right. the failure occurred while the car was parked. i had adjusted the seat forward to my usual driving position, and pushed backward on the seat to check that the adjuster was locked. when i did that, the seat bracket broke loose and the seat tilted back and to the right. i have replaced the broken rail, honda part number 81660-s2a-a02. i previously replaced the right side driver's seat rail (81670-s2a-a02) when the adjustment mechanism jammed, in january2011. that part is no longer available new from honda. all bolts were reinstalled according to torque specifications in the honda s2000 factory service manual.