I have been on some Class 142 in the past that looked quite bad internally on parts of the flooring and around some of the windows. Not a depot cleaning problem, as cleaning can do nothing where floor covering has worn away in areas.
Regarding the very cold winter Class 142 internal temperatures, my wife and I went on an early Saturday service which was on a diversionary service pattern that had started somewhere in the Wigan area, called at Manchester Victoria (platform 6) where we joined it, then via Rochdale, the Copy Pit line, Accrington, Blackburn (reverse) and Clitheroe. It was cold on the Pacer when we boarded and we were utterly freezing by the time we reached Clitheroe.