Seal Gap in Flat Felt Roof

I have a gap in my garage roof (flat felt) at the very corner where the felt has been bent over to form the right angled edge. The gap is about 30cm long and up to 2cm wide in places. It is directly over the corner of the garage and although water isn't getting inside it's soaking the brickwork (and timber joist) each time it rains.

Are there any sealant products I can use to fill a gap that size, in slightly damp conditions? I could cover the gap up for a while before sealing it, but it won't be dry until the weather picks up.

I'll post a picture tomorrow showing the gap and brickwork.

I would cut a patch of roofing felt, slightly smaller than the gap, then coat the whole area with the stuff I've got in a tin at home. (I'll post the brand of it tomorrow when I get back )

Just warm it up with a blowtorch, and press it back into position.

Not the greatest picture and the crack seems more like 1cm at its widest point now I look at it again. Maybe that's small enough to fill with some kind of sealant directly?

The stuff I've had a lot of success with is called "Flexacryl" - made by Laybond.

Here's some:

http://shop.parkerbs.com/product/LAYBOND_FLEXACRYL_BLACK_2.5KG_R00168