When you look at the map you see every sector is linked to some isle on the map.

There are undiscovered isles without sectors near 3,4,9 and 11... maybe start searching there.

HMS Moneysink failed to find Sector 7 again (after 4 Trips to 5 with different setups) with full invincible parts and lvl18, other discovered this sector with lesser grade ships and lower level.

Now trying my old "hulk" build with low range/speed and high retrieval/favor/surveillance... if this fails i will try tomorrow a "known" route from the spreadsheets which found this sector.