During the half-term week's running in October, when Stepney ran on the trains with Fenchurch, corrosion holes appeared in the base of its chimney, and eventually it became possible to see right through it.
This chimney was made during its repair in 1982. It has been replaced by the chimney from 32635 "Brighton Works", which is a Marsh cast chimney with a copper shroud fitted around the cap.
A new chimney is being constructed using the same technique as was used for Fenchurch's.
Update on Sunday 2 December: Stepney's boiler has suffered a crack in the firebox backplate, just above the foundation ring between the corner and a mudhole door. A groove in the plate has formed inside, so the repair technique will be to cut out and replace a small section of plate. This part of the boiler is immediately in front of the trailing axle, so the trailing wheelset has had to be removed to gain access to the area.
More pictures can be found here.