Not sure on the Sealand, however on the Thetford Aqua-Magic 5 that I have, it was the "Water Module Assembly" that was the source of the leak. Although it appeared as bad connections and even a bad flange seal...
There apparently was a defective batch of them as I replaced it with new twice and finally read about the defects. I bought my last from the big river in South America and no problems since.
If it is an assembly such as mine, you can not see where the actual leak comes from, merely where the water goes...on the floor around base of toilet...
Good luck!