The trigger for the refueling point is of by a train length, 198yds, The trigger has been setup for the rear of the train but the distance marker is been calculated from the Engineers seat. Further more, it does not matter where you stop, the game then goes into the Refueling process but this does not work if the refuelling hose does not reach if the player has stopped to far away. Fuel tank should be aligned with refueling position before refueling process starts. Player can complete scenario.
This is a very old and often discussed misguided development, which has been carried over from TSW2020. I think it needs to be revamped from scratch, but we users will then have to adapt to it once again.