Dishonourable mention here to the Class 303 transformer explosions, necessitating a very hasty return to steam-hauled services while things were sorted out
As something of a bookend to this, a few 303s were withdrawn in the ScotRail (NX) era when fires started in their motor coaches. Not sure if the transformer was the source, but if
this page is accurate, at least 4 303s are noted to have met their end in this way as the operations of the class were being wound down leading up to December 2002. These were (in order of occurrence):
- 303058 - Blantyre - September 2000
- 303010 - Bishopton - December 2000
- 303054 - Bellshill - March 2002
- 303009 - Springburn - August 2002
Also, the linked page notes that BR instituted a rule in 1991 that no 303 with it's pantograph raised was to be left unattended for more than 15 minutes after a fire eariler that year started in unit no. 038's motor coach (which left it a gutted wreck and damaged the units around it) after it was stabled at Shields Depot with it's pantograph up.
On the whole however, despite a rather ignominious start and the above incidents in the type's twilight years, the 303s served Glasgow and it's environs with little in the way of fuss for over 40 years. Hardly a suitable candidate for this thread in the grand scheme of things.
The 334s were pretty terrible during the first few years. Sometimes a train would go out of service half way down the Ayr line and everyone would be chucked off at Kilwinning. It was pretty common for a driver to "reboot" the train while stopped at a station. I remember sitting in a pitch-black 334 with the doors locked and the lights off while the thing rebooted. You knew the reboot was finished when the incredibly noisy ventilation kicked in.
They've improved massively since the early days, and as far as I know their mean time between failure is pretty decent these days.
Also, and in line with their 458 relatives, their introduction was heavily delayed (originally slated for 1999, in the event April 2001) as attempts were made to rectify the numerous faults. This delay forced the remaining 303s to remain in service for quite a bit longer than originally intended and, as you note, it took a good few years for their availabilty/reliability levels to reach acceptable levels. I've never had one 'sit down' on me across the numerous journeys I've made with them over the years and, while they're not perfect, they're far from the worst.