61151 was one of the Optare Prisma-bodied Mercedes O405s which formed part of a very large Mercedes fleet at Oldham at the time (14th August 2004). The high-level viewpoint shows very clearly the air-conditioning unit fitted on the roof of these vehicles. However, since the roof light and hopper vents are all open, one can surmise that it was either not working or not being used very efficiently.