Screen bolts.

Following the recent down poor I noticed a good deal of water flows through the screen bolt area (particularly on the off side). As a Summer job thought I'd remove them, clear the rust away and put it all back together. Any time honoured techniques etc?

My local LR firm mentioned a black non-hardening tarry substance for filing holes (not silicone). Where do I get this?

The black stuff mentioned could be called Dum Dum? The cheapest I found it online was at Eldro Dum Dum Sealing Compound at www.car-spot.co.uk
I am no expert but I have just removed my windscreen frame but thats a roof off job.
I stand to be corrected but I would remove the 3 bolts and the windscreen hinge just comes off with a slight tap. EACH side has 2 gaskets on the outside hinge, one has 2 holes the other has 1 and they are likely to be shot. Part numbers MXC9982 and MXC9983.... Thats for a 1994 Defender (have my invoice for mine in front of me from lrseries)
Just clean the bolts and the hinges so they sit nice and tight... new gaskets and maybe a little extra flexible sealant around the bolt holes on the gasket, refit.... thats it.

Any good motor factors will sell you a tube of non hardening Panel sealant. You can just take the roof bolts out and the windscreen will come off with out having to remove the roof. or just slide it back a couple of inches.