I just happened to look up at the globe light in our bathroom last
night, and noticed that it was half-full

Outside
=======
From outside this morning, with the aid of binoculars, I cannot see any
tiles missing or slipped.

It's *conceivable* that the water got in yonks ago, and I've only just
noticed it: about 6 months ago I did notice a tile that had slipped,
on this line in the roof; I shoved it back into place with a long pole,
and it's still properly aligned with all other tiles.

Prognosis?
==========
I don't yet know how bad this is: next time it rains heavily I'll be up
in the loft looking. The water in the light may have been there for --
ooh - weeks? months?

However the rafter concerned is damp and has a slight case of wet rot
where the wood meets the roof felting -- mostly it feels sound, if damp.

Remedies?
=========

I'm proposing to spray the rafter with Thompson's Water Seal: it's all I
can think of doing so far! Apart from looking for a leak, next time it
rains heavily.


History
=======

This is a 1962-built house, far from being a Rolls-Royce build, but not
jerry-built either. The tiles are concrete. The roof is orientated
exactly East-West, and the leak is on the North side, which is quite
heavily mossed.


Any general advice, or experiences, that anyone can offer?

Cheers
John