During the pre-landing checks, the pilot noted that no pressure was available from the left brake pedal. The strip has a slight slope, and the pilot elected to land up the slope in light quartering tailwind conditions. The aircraft bounced twice after touchdown and the pilot commenced a go around. The aircraft veered off the strip and collided with several trees before coming to rest 50 metres from the centre of the strip. The left brake had lost pressure because a worn seal had allowed air into the brake line. The pilot advised that the brake problem did not affect the selection of landing direction. It was considered that directional control was lost during the attempted go around, when the aircraft was affected by a wind gust at a critical stage of the flight.