I managed to sort out this problem after gaining confidence from Bob F and some additional PDfs he sent (Thanks Bob).
The new Sirion is a bit different to the old because it has electrical door locks and a different door panel arrangement - a top and a lower panel with an armrest panel attached to the lower panel. So, to remove door panel:
1. Remove small screw by door lever and in door grab slot.
2. Prise up and lift up the top panel (armrest). This feels like it will snap but it doesn't. Unclip the door switch cable before you remove the armrest panel.
3. Remove large screws holding panel to door
4. Prise off lower panel which has the dreaded door clips securing it to the door. Take care not to snap the clips - I just tugged each location sharply and had no problems (daihatsu use better parts than most)
5. Once the lower panel is off, check that the lower clips still have the thin rubber washers in place, or check they are not stock to the door panel (if so, put them on the clips instead - don't lose them as they are water seals)
6. This is when I saw the source of the leak. The plastic liner is stuck to the door by black butyl sealant strip and the inevitable creases had coincidentally been located at a low point and the butyl had slowly lost its "stiction". I bought some 10mm diameter strip from eBay at £6 and then slowly stretched it to be thinner about 5mm diameter then applied overlapping strips to reseal. It's great stuff - sticks to anything, including itself and is a bit like BluTac.
7. refit the panel

I repeated this for the other front door with no problems and the leaks (which in the early days were causing condensation) have gone, together with condensation problems.
It's been fine for about 10 months so I think I've cured it.

Colin
(I love the new shape Sirion)