[danielsatur]

1) Strategically place a garden hose with a little water pressure in the trunk gutter & let the water roll to pinpoint your water problem.
2) Open trunk
3) You can do the left side trunk, right side trunk, and do both by placing hose in the upper center.
4) Once you rule out the trunk seal, and rear tail lights, lets focus on the lower/upper rear window.
5) Use Home Depot/Lowes Doors & Windows sealant for quick fix, or
use masking tape with a little WD40 on your finger tip to make a nice finish.

Note - If you suspect the rack on the trunk lid, do the outer trunk lid before doing rear window.