Scout Boot Leak?

After having had our new Scout for a week, I decided to give it a good clean, especially as the dealer hadn't done a particularly good job of it (traces of polish residue, or something similar, all over the car).

A couple of days afterwards (following a heavy rainfall), I noticed a damp patch in the middle of the boot, almost directly below where the roof meets the boot lid.

I reckon this could have come from one of two places:

1. Water ingress through the seal around the boot lid, either from a dodgy seal or a careless blast of the pressure washer;
   
2. Leak from the rear washer.
   

Fortunately we've got a boot liner, so there's no danger that the water's going to go anywhere else. There wasn't a noticeable screenwash smell, which makes me think it's more like to be water (hose or rain) getting in somewhere.

Anybody had this happen to them?