Rather than fill the gutters level with sealant I used lengths of L shaped plastic (B&Q) and bonded them to the Hi Top Lip that sits in the gutter and sealed both ends. The Gutters are thus fully sealed. Following all the heavy rain I removed the interior High Top panels and so far so good, no water.
The Autohomes high top is bonded along the gutters only with the front and rear having seals. I have left a gap at the rear corners to allow any water that may get in a means of escape, you can see the gap in the picture just above where the rear of the gutter ends
