2008 Yaris, Hatchback - Both rear brake/combo light assys leak

[beowulf]

I have a 2008 Yaris, Hatchback (with manual transmission),
and was troubleshooting a problem with rain water leaking into the rear and collecting in spare tire well and soaking the carpet.

I have removed the right, rear combo light assembly and verified I have the same problem as identified in this video:
https://www.youtube.com/watch?v=5leyRVSVbZI

Any suggestions for how to fix it?

I'm thinking I could try to clean up the area (sheet metal, combo light assembly, and gasket) and try to seal the existing gasket with some silicone or buy replacement gaskets?

I think these are the part numbers for the gaskets:
81554-52530, GASKET, REAR COMBINATION LAMP BODY, RH
81564-52470, GASKET, REAR COMBINATION LAMP BODY, LH

I'd appreciate any input. I'd like to fix this one right the first time.

Thanks,
Steven