I have a leak in the top left-hand side of my windscreen in my P38. Has anyone had a a similar problem?

Yep, but never got to the bottom of it....it was either a failed windscreen seal or where the roof is joined to the sides of the roof where the roof rack rail is and was leaking there....

I did try using a whole shed load of sealant in the area but that didn't solve it either!

Yes mate. Had the same problem for a while. It’s very common. Can’t guarantee this’ll work. This is what I did to stop mine. Pull the head liner down and seal along the back edge or the screen. Also take the top screen trim off on the outside(order some clips as they’ll break and seal along he top edge of the screen. Take the N/S outer S pillar trim off. The 4 screw holes that are used for the trim have foam backs. They disintergrate so pull them out and put some sealer on the back of them too. Should help. I used tigerseal pu sealant.
https://www.google.co.uk/search?sou...131k1j0i46k1j0i10k1j0i22i30k1.112.313PU5lS6ys

Mine was the same until I had a new windscreen and it's fine now.

New screen did the job on mine to