W123 240D: Windows foggy on inside = heater core leak?

[anghrist]

Hey guys. This is a situation that has vexed me and my girlfriend for some time now. The windows have a substantial oily fog on the inside, even after cleaning, in the middle of our desert 110 degree summers. After an hour or so of driving, I will get out of the car and after going inside and cooling down I notice that my clothes smell strongly of coolant.

This leads me to believe that the heater core has a vapor leak, since there is no pooling of coolant on the floorboard of the vehicle. I know that very few attempt replacement of the heater core due to the difficulties involved, but for those who have...

Do the water pipes that go into the heater core have simple o-ring seals or is there any seal at all?

I have a replacement heater core that I plan to have cleaned and pressure tested, but if the seals need to be replaced, which should be done anyway, I would like to know what I will need before I get in there.

Thanks for the help.

Josh