[mobius]

Smarkwilson, you might not have to replace it. But what I would suggest is to tear into it again and check to see that the connector is flush with the back of the head. When I used one of the cheaper copies of the OE part no matter what I did (until using a pry bar on all the edges) I could not get it to sit flush with the back of the head which means it wasn't seating properly. If I had left it that way there could have been either a slow or major leak out of the bottom of the connector. I wouldn't have noticed this had I not taken the time to look around the connector with a mechanics mirror. It is a lot of work but better to be safe than sorry when dealing with the cooling system.

I think most people wouldn't catch it either unless they were being careful assuming the two bolts seat the connector properly which they don't. Like I've said before BMW really should have had 3 or 4 bolts on the connector to make it seat properly without any hassle. The best suggestion though like someone else has said is to absolutely coat the connector edge with dielectric grease so it slides in easily.

A pin hole wouldn't do that. The BMW cooling system is supposed to be completely sealed so it can build pressure. Have you checked the dual temperature sensor for the cooling fan? If the cooling fan isn't working properly additional pressure builds up because of the system not being able to cool off. You'd notice this in idle traffic especially. I firmly believe this is also the reason why the expansion tanks will literally burst or explode sometimes. When they are old the plastic has deteriorated eliminating the built in safety factor they are engineered with which combined with an increased pressure over spec, causes the bursting. I haven't run any scientific studies to prove this but as an engineer it's my best guess.