small hole in slate.....how to seal?

[Joystick]

In my brother-in-laws house that he rents out, there is a very small hole in a roof slate that is dripping on to the front supporting wall - this is then leaking out above the window frame on the ground floor!!

He cant afford to have the slate replaced at the moment and the hole is very small (less than half a penny).

I indented to crawl to it (it would have to be where the roof meets the wall!! No boarding either!) and fill with an adhesive waterproof sealant.

This is only a short term fix, but is there any particular products available that are best for the job?

 

[cotswoldbuilders]

It would be more practical to get access from above, then slide a piece of lead up under the slate and cover the hole.
It will last longer than mastic from below, plus a better job.
One slate wouldnt cost the earth, remove the broken one and slide a new one in, fixing by a lead strap.
If you dont have a slate rip, use an old wood saw, cut an angled notch near the tip to slide up and yank the nails out.