On the subject of old units that lasted until relatively recently, the
'Thumper' DMUs:
Stalwarts of the branch line to Uckfield right up to 2004. Much as I like an old train, I don't remember the Thumpers with much affection: they were draughty, noisy, bouncy and - by the time they were withdrawn - chronically unreliable.
They were also non-corridor, and in some parts of them there was no toilet, which posed a problem for me on at least one occasion when one had gone wrong and stranded us at Oxted to wait for the next train. I'd gone for a couple of pints in the pub by Oxted station and then had to dash back to the station without nipping to the loo. The photo still exists of me standing up on the seats pissing out of the window.