The message
from Al 1953 contains these words:

Hi,
I have a garage with an old corrugated asbestos roof. The roof has a number
of small holes where the rain gets in. Also, a draught gets in through gaps
where the sheets overlap. Would expanding foam be suitable to plug these
gaps and holes?

Expanding foam fine for along the edges of sheets if used from the inside.

For small holes, cracks etc. Any sort ofd scrim with several layers of
thick bituminous paint. Stick it into the first layer and then paint
over several times.