Thanks for all the responses folks.
When we buy 2nd hand, of course we have to accept that further costs may be involved. What I find bewildering is 'Hifi enthusiasts' acceptance of really expensive kit failing.
My original post mentioned a midi system that has never gone wrong. Average sound but obviously stable. I cannot say that about loads of components that cost a shit load more. Amps that keep blowing valves, capacitors failing, CD players that fuck up reading discs or their mechanisms just don't function properly. The longevity of a lot (not all) is a fucking disgrace considering the money that was paid.
I've got a shitty old kettle that's asked to boil water probably 20-30 times a day. It still does the job as well as ever after prob 20 years. No repair whatsoever.
I think it cost about £20.