I have tracked down the source of a significant leak in my 12 year old
Bosch dishwasher. There's a worn O ring on the water inlet side of
things. It's a fairly chunky O ring about 2 cms wide.

https://i.ebayimg.com/images/g/EzcAA...7j/s-l1600.jpg

Bosch still sell these, but annoyingly they charge around £25 for a set
of 4.

I don't think it's possible to silicone the joint. Any other suggestions?

The machine has been used once or twice a day for 12 years, and I was
happily contemplating a new Bosch to replace it, but the price of this
simple spare has put me off.