1994 Trophy VW

On a T4 with a high top, there are really only two likely possibilities in that location - one being the join between the A/S high top and the body, and the other a leak in the windscreen surround area. Of these, the latter is far more likely, in my opinion. I ~think~ you can rule out the door seals, because it's hard to see how it could get that far forward, and door seal leaks tend to track round the door opening anyway.

It can be quite difficult to work out exactly where the source is, and I think it's not unknown for people to have to remove the windscreen to find out for sure. IIRC the windscreen is bonded in on a T4, so it may just be a slight fault in the bonding. At the other extreme it can be serious corrosion hidden in the windscreen recess.

I had a similar problem on a Transit-based A/S conversion and was fearing the worst, but actually it turned out to be just an accumulation of crud at the bottom of the screen, which was causing rainwater to seep up through a fault in the screen bonding by capillary action. First step was to clean out the crud with Q-tips, and the second was a couple of applications of Craptain Crolley's Creeping Crack Cure, and it never caused a problem again.

[Edit: the other main area of leaks with that roof are the high top windows - but I don't see how water could track that far forward unless your normal parking space is nose-down on a mountainside...]