Time to get that window out and the surrounding aluminium sheet out of the way. On this window there is a little rubber strip (pressure strip?) that needs to be carefully peeled out before you can remove the window.

Put it somewhere safe as you will be wanting it again when it comes to putting the window back in. My brother then came to my aid and with me on the inside and him outside we gently started in one corner and eased the rubber back..at the same time I gently applied pressure to the window to ease it out of the frame. Window, and rubber came out in one piece leaving a clear view of the wood underneath.

There is a little damp area in the corner of the frame which initially doesn't look too bad.

I have to get this skin of aluminium off now. I start by taking off the running lights. What on earth was Mr Botchit hoping to do with this splotch of mastic? The other lamp was the same. Nothing to stop the water coming in at all.