Rainwater down the backside of the gutters.

I have a hip roof with two layers of composition shingle roofing.
The last layer and the continuous aluminum gutters are 15 years old.

I have rainwater dripping down the backside of the gutter along a section
about 15 feet long.

I'm afraid to pull up too far on the old shingles, but it appears that
the lip along the backside of the gutter that sits on the roof is raised up
about a quarter inch. Assume they did that to level the gutters...but
who knows.
Anyway, over the years the shingles have sagged so there's a valley in
the roofing
that collects standing water. I'm thinking it seeps between the gaps in
the shingles
and ends up on the wood roof and drips down behind the gutter.

What are my options for fixing this?

The proper fix would be to remove the gutter and bend the metal so it
sits properly on the
roof. But it's an inside corner and I can't see how to get it
apart...and back together
so it doesn't leak.

I could trowel tar in the valley so the slope is monotonic and there's
no place for water to collect.
Not sure what other problems that would cause.

I could lower the gutter so it sits on the roof. I'm assuming the
shingles would
straighten themselves out without cracking??

Suggestions?
Thanks, mike