United Auto Leyland National 3102 LUP902T. Delivered in July 1979, entered service, destroyed with a number of other vehicles in Durham depot fire about 3 days later. However, beaten by three brand new Atlanteans delivered in 1976 to Trent’s Derby depot and caught up in that depot fire. 571 was damaged but was famously rebodied with a bizarre Willowbrook body but 573 and 577 were destroyed without entering service! Don’t know if that constitutes a working career? Think Southdown lost some nearly new VRs at Hove in a fire - depots fires very seemingly common in the 1970s/
Of course, there were plenty of examples of changing views and requirements leading to whole tranches of vehicles being withdrawn. London were experts with AEC Merlins and DMS class Fleetlines all going early - the first Fleetlines were scrapped at 9 years old. London Country were withdrawing Leyland Nationals at 7 years old. With MAP schemes and single deckers going out of style, many NBC firms withdrew Leyland Nationals, Bristol LHs and REs, and assorted Ford single decks prematurely as well. Seem to recall that NBC bought quite a number of Duple bodied Ford R1014 buses and many went in five years!