I've seen some gen 2 lights leak where the lense is attached to the housing, it's been sitting out in front of the car for 20 years. The clear square cover behind the low beam has 4 tabs that break allowing moisture/water in, very common. All the bulbs have a rubber gasket that seals them. If they have been changed to after market bulbs, mostly low beam, this is where I'd look first. Pressure testing on the bench, I found leak where signal light plugs in. Air comes right through the bulb housing when it's not plugged in to the car, and there is an oval rubber gasket on the plug. 3 bolts, and 1 screw, and the light comes right out pic of LB cover