The phone has moisture sensors inside. If the moister sensor is tripped the warranty is invalid. Does not matter if the seals are damaged. Here is the section from the Note 8 Warranty document.
Maintaining Dust and Water Resistance
This device is rated IP68 using the Ingress
Protection rating system. The device has
been tested in a controlled environment
and shown to be water and dust resistant in
certain circumstances (meets requirements
of classification IP68 as described by the
international standard IEC 60529 - Degrees of
Protection provided by Enclosures [IP Code]; test
conditions: 15-35°C, 86-106 kPa, 5.0 feet, for 30
minutes). Despite this classification, the device is
not impervious to water damage in any situation.
It is important that all compartments are closed
tightly.
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Note: If any liquid is found to have entered
device components or an internally sealed
system, this condition will void your device
warranty