was introduced in each set, this was marked on the exterior of the doors by a magenta and white sticker. On 19 April 2004, the unusually large rate of increase in atmospheric pressure led to an airlock and failure of hydraulic pressure on eight of the Class 357 trains which caused their computer's software to lower their pantographs and so be unable to collect power from the overhead lines, causing service disruption. After their technical problems were sorted out, they have since been the most reliable fleet of EMUs in the United Kingdom, winning Best Modern Era EMU at the Golden Spanners Awards from 2005 to 2007, for an average annual miles per casualty (MPC) figure of 43,180 in 2005, 37,391 in 2006, and 45,459 in 2007 (defined as the number of miles a train runs before a defect develops causing 5 minutes or longer delay). The Class 357 units are all normally maintained by Bombardier service technicians at c2c's East Ham Depot, which won the Golden Spanner Award for Maintenance Team of the Year (Rolling Stock) at the Annual National Rail Awards in 2005 and 2006 and their Shoeburyness depot. In December 2005, c2c's East Ham depot began putting advertising vinyl wraps on some carriages, starting with branding the MSO intermediate trailer car 74716 in set 357216 as a 'Cough-Free Zone' by the cough syrup makers Benylin for the winter. In June 2009, c2c and Bombardier began a repainting programme on the Class 357 units beginning with 357203. When the vinyl wraps were taken off the Class 357 units, slight corrosion caused by water getting trapped behind the vinyl was found in the aluminium around the doors, so a bodywork maintenance and repair programme was carried out. The corrosion was treated by rubbing the aluminium down and repainting it with two-pack paint. More serious corrosion caused by water seeping in through a poorly-sealed join between panels was found behind several panels on the lower part of the vehicle bodysides, which had spread to the outside. A thick, tight mastic seal was introduced between the panels to prevent this issue from re-occurring. To save money during construction, stainless steel bolts were used to secure the external aluminium panels in place; however, this resulted in galvanic corrosion of the more reactive aluminium, so the bolts have been replaced by aluminium ones. Salts in water catalyse corrosion, a problem for the c2c