oddbean Buy a new element, it’s only worth getting Gabor to fix the older pre 80s elements as these can no longer be purchased.
The seller is full of it, the new electrical wiring and switch are a clear indication he knackered the element previously and hoped changing the switch and wires would resolve the problem.
If you’re confident with the electrics, you can swap it yourself otherwise there are a few servicing centres in the UK that will swap it for you and probably won’t charge much to do it. I’ve used Frank at Ferrari espresso in South Wales who’s great, The espresso Shop in Glasgow also do it and I’m sure there are a few more.