Record where the water begins
From a safe dry location, note whether moisture appears at a corner, across the entire bottom or at the section joints. Record whether the door was closed and whether water was pooling outside. Keep the observation tied to one rain event; several different paths can leave a similar floor stain.
Separate sealing from site drainage
DASMA’s threshold guidance explains that slab details affect water entry under a sectional door. Replacing a torn seal can address that material, but it does not correct every slope or runoff problem. Ask the assessor which evidence supports door work and which conditions need a building or drainage specialist.
Define the expected improvement
Have the proposed remedy and its limits written down. Sectional doors should not be treated as flood barriers. Avoid storing sensitive items where past water has entered until the source is understood, and do not operate electrical equipment exposed to water.
Your questions
Will the thickest available seal always work best?
No. The seal must fit the door system and site conditions without interfering with safe operation.
Should I test the door with a pressure washer?
No. Forced water can create an artificial condition and may damage finishes or components.
Can a larger bottom seal fix an uneven garage floor?
A different seal may not resolve an uneven slab or water approaching from outside. Have the door’s closing position, seal fit and floor condition assessed together; do not increase opener force to press the door against a low spot.