Water coming in from gutter

I have a 1998 Boxer Autosleeper harmony and have rain water coming in top left of windscreen passenger side.  I had the windscreen checked and its not that.  If I carefully pour water into the gutter, it comes in under the roof lining and drips down into the passenger door pillar and onto step.  It appears that its the junction between the fibreglass high top and the vans metal body.  The black guttering that runs around the van is sealed when factory fitted so I have no clue to resolve it.  Does anyone know how/who can help?

Roopert wrote:I don't know of any easy solution. There have been previous threads here about similar problems, and at least one of those involved taking the roof off. But you obviously need good facilities to be able to do that (the owner in question had a barn).

First thing I'd be inclined to do if it were mine is to remove the cab headlining and see what you can see when that's out.

That's a good idea. I hadn't thought of that.  I had another good look at it yesterday and even though a windscreen specialist said it wasn't the screen, I think it still might be the bonding gone.  I got up there with a watering can and carefully filled the gutter. The water started a steady trickle up in the top corner from between the windscreen and the windscreen frame. It drips onto the head lining above the sun visor and down onto the wheel arch cover, and pools in the door step.  So in the first inst, I might get a second opinion from anther windscreen fitter. Thanks for you suggestion which I will consider if it's definitely not the windscreen.

I have siliconed all around the top corners on the outside around the trim and it still leaks.  Its difficult to see whats goiung on because the 2" wide black gutter wraps around the front about a foot and sits tight up to the top of the windscreen rubber trim. Thanks though.