Power washer (Huddersfield HD2)

I was gifted this by a relative a while ago who told me it was a prototype power washer.
I’ve plugged it in to check that it works, which it does.
It is leaking from where the pressure hose clips in, but it looks like the rubber ring/washer is missing (from the third photo).
It’ll need a clean as it’s been sat at the back of the garage for years.

Fair Chance Policy: I’ll wait before choosing a recipient to give more people a chance to reply.