on all of these body styles during this era, the seal at the bottom of the rear glass does not last, and when the car is parked downhill, rain will run over the sheet metal between the trunk gasket and the rear glass, and allow the trunk to fill up with water.

1st locate the scource or origin of leak.
when the trunk is dry & there is no trace of water
test with a cup of water. spilling 8 to 10 ounces over a small area of the trunk at a time. Between each cup of water look for water leakage. After determining where the leak is coming from. Evaluate the amount in which it leaks. If it is a minor leak, weather stripping for doors will slow it down. For a major leak 100 % silicone caulk, plus weather stripping should do the trick. Apply the caulk in a line bead. If it is a huge leak u may have to apply a lot, then run ur finger along the leak to smooth out the caulk. Another method is to apply a bead at a time which will take more drying time in between coats. (day per coat)

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