Whenever I wash my 1971 142, I accumulate water in the trunk in the wells behind the rear wheels. The trunk has a new gasket and I have smeared the gasket with silicon grease using the grease imprint on the matching body face to confirm that the gasket has a good squish contact area with the body, so I don't think gasket leakage is the problem. I initially discovered that the seam sealant on the ends of the drain box under the rear glass had separated and was allowing significant amounts of water to enter the trunk at those points. I completely removed all the old seam sealant and resealed and that area now remains dry. That greatly reduced the amount of water; but, I am still accumulating about 10 - 15 ml of water in the well on the driver's side each time I wash the car. The passenger side is remaining dry. The water now appears to be entering from somewhere around the taillight area or the back edge of the trunk over the taillight; however, after repeated poking around forays and sealing likely locations, I have not been able to suss out the location of this final leak. Does anybody have any suggestions as where to check?

Full disclosure, I do use a pressure washer; but, with the pressure turned down.

Further testing suggests that the water is entering the trunk under the lid at the rear corners just above the taillights. The problem appears to be caused by the lap joint where the rear wall of the trunk is attached to the rear quarter panels. This horizontal lap joint is visible about 6 " in front of the taillights along the edge of the lip on the trunk opening. When the trunk lid is closed, the trunk lid gasket crosses this lap joint. On my car, the lap joint is slightly depressed. When the trunk is closed, this depression creates a gap below the mating surface of the gasket. During heavy rain, water runs down the channel on the outside of the gasket and then slips under the gasket and runs down the inside of the gasket to the back corner of the trunk where it is blocked from draining to the outside by the gasket, so it pools and then runs over the edge of the trunk opening collecting in the wells behind the rear wheels.

Testing with smeared grease, the only way I can get the gasket to seal over this lap joint is to adjust the strike on the trunk latch so that the lid sits much lower providing more gasket compression. This makes the lid very hard to close because of the excessive gasket compression plus the lid is no longer level with the body on either side of the lid (big time misalignment). Not a satisfactory solution. I am thinking that the solution might be to try fill in the depression at the lap joint with a little clear seam sealant to create a level surface for the gasket to seal against.

Old timer trick. Buy some cheap baby powder. Clean out the trunk. Sprinkle the baby powder on the verticle surfaces where you suspect(or everywhere). Close the trunk and water it down. The water entering will leave a "snail trail" where it is entering. This method has saved me hours searching numerous cars whether the trunk or floor board etc.
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Post Back. That's whats makes this forum work.

I will give that a try next time I wash the car.

Or get inside the trunk with a flashlight and have someone hose down the outside.

Note: the person that closes you in the trunk needs to be someone you trust to let you out.
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

Been there done that, doesn't work. Baby powder
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Post Back. That's whats makes this forum work.

Tried the baby powder. Seems to be coming in somewhere around the taillight bucket or sneaking in under the trunk lid right over the taillight. However, the baby powder I used does not cling well enough to vertical surfaces to get a good trace. I may try cornstarch which seems to be a bit more clingy although wet cornstarch might prove to be a good growing medium for bad stuff.

So......rules out my wife and off-spring?