If your car is like mine, the aluminum trim cannot be removed unless the whole window is pulled. Instead, I used a popsicle stick (or use anything that general shape) with cloth over it. Force it under the rubber to clean out the crap that collected there. I used alcohol as a solvent. Keep going until the cloth comes out clean. Then seal it by raising the rubber slightly and force a bead of sealant in between as you move along. Better too much than too little, as the extra can be trimmed away. Mask the painted areas though.

Before you do any of that, make you really have a problem there. Rust and/or moisture under the window in the trunk are a dead giveaway. And once again, the correct way to fix this is to reinstall the window with a new seal and repair the rust areas. The above is a low-cost shortcut.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma