Our ancient (for modern consumer electronics/white goods) 20 yo Hotpoint washer was being a bit picky about how the door was shut. Sometimes it would wash, sometimes it would need an extra push on the door - and since we have Economy 7 and the washer goes on in the wee small hours (aka the small wee hours) we would often wake up to a machine that hadn't washed.
Diagnosed a faulty door interlock switch. Looked up new one on the web and I thought it was £20. Not being sure if the lock was the problem, found one on Fleabay for £8, delivered. Just in case it wasn't the lock.
Fitted the new (old) lock, only took me 15 mins, having determined just how to get at it. Works fine. Result.
In browsing for motor brushes (it's bound to need some soon) I saw that the price of a new lock wasn't the £20 that I thought it was, but £7.65. So 35p cheaper (but without p&p) than a used one that's only 2 years newer than the machine itself. Doh……..
Oh well, at least I now know that the problem was a duff interlock, and I know how to swap it over for the inevitable new one. Assuming that the next machine problem isn't terminal. But even major parts such as the programmer and the motor, still available new but >£100, are available used at around £25 - so maybe the machine has a few more years left in it yet.