Would have been easier to get a train from East Dulwich Station to London Bridge direct. With regards to the 40, it may have possibly broke down en route.I have noticed a number of buses in London breaking down recently. Was the 40 still showing on the countdown monitor throughout the duration of your wait? Also my rule of thumb is after 20 mins of waiting, find an alternative route. most of the time buses that are running quite late tend to simply "go out of service" to get to the garage for the next shift.