Our 1960s house has a corrugated roof of what is presumably cement
asbestos.

The roof is intact but there is some water ingress. I suspect this is due
to water entering through joints rather than permeating through the
asbestos cement.

The roof is under a 60 feet high tree and has quite a coating of moss and
twigs. Removing them would be difficult without risking breaking panels
and the moss etc probably cushion the panels against falling dead branches.

Any ideas of how I could waterproof it from the inside?