Anyone recognise possible causes, leak staining / hotpoint

Leaks can be very difficult to find. As you have mentioned, the point at which water drips is not necessarily the place it is leaking from because water could be running from much higher up. If the marks you have photographed are definitely water leaks then the main suspect is likely to be the door seal where it attaches to the outer drum. But it could be leaking from the outer drum itself, especially as many of them now have 2 halves of the tub sealed together. You could also try examining carefully all of the inside of the door seal. Check to see if there are any small holes anywhere at the sides are at the top or bottom. A door seal can leak from the flange that presses against the door glass, at the point where it attaches to the out of drum, or through a hole or slit in the rubber between the 2.

If you can't see anything it might be necessary to take off the door seal. Once off you should be able to see if there is a watermark running down the front of the drum from the point where the door seal attaches. Whether or not you decide to try taking off the door seal is up to you. It can be relatively straightforward or it can be quite difficult depending on the machine.