Plastic utility room roof

After decorating the utility room I'm cleaning the plastic roof and redoing the silicone on all the plastics. I have noticed very small flies in between the two layers on the plastic roof. How are they getting in? I have no access to the lowest part of the roof as it borders the neighbouring property. To say we dont get on with them is an understatement!

Will something need sealing at the bottom of the roof where the guttering is. It's like a lean to/pitched plastic roof from the house into a guttering

They are normally taped with a breathable tape to stop this happening.

Taped at the gutter end. There is a piece of lead flashing that goes across the top of the roof where it goes up to the brick wall of the house

I’ve seen flies inside the flutes even with both ends taped. I reckon they lift a bit of tape and let themselves in.