Thanks, PrecisionMachinisT. Sounds like something I'd want to get a
professional involved in, probably at the time it actually does leak.

Indeed, advice like "don't walk on it" isn't helpful, as it is necessary to
unclog the gutter drain to clear the pools of water on occasion.

Sounds like a 'hot tar roof'....

If it leaks, just have some more hot tar put on it--this time put on lots
of
it, and also maybe some rocks / pebbles to make up for temperature
expansion/ contraction.

--

SVL