So I've played around PS little bit and I think I've solved your problem. Unfortunately shorelines has to be corected manualy, everything else can be automatized.
This came out from stitching screenshots together
after repairing shorelines I've selected all blue pixels (with magic wand tool, tolerance 150,
AA turned off) then contracted selection by 4 pixels (in order to preserve original shoreline waves and details) and hit delete. Result:
Then I've created new ocean from single screenshot. Water tiles are repeating in chunks 32x28 pixels with some random variations in wave pattern. And finaly whole sector with new ocean
Here you have ocean pattern. It can be stacked in both horizontal and vertical axis without any seams