RTH - thanks for the follow up
I wondered what had happened to you.
I thought I had resolved the pressurized cooling system problem with my 300D but it still remains pressurized overnight occasionally. It seems to have alot to do with ambient conditions. When it is cold it seems to retain pressure. Then when it is hot (low 70's dF like it was today) it does not retain pressure. Anyway, when I got home this evening I removed the cap and relieved the pressure. Later on (I again opened the cap and it was almost as if it were pulling a slight vacuum which is what I should have seen seeing as how it was cooling down) I went out, cranked it up and ran it for a few minutes to see if it would build pressure in a real short period of time it did not. I would think that if it had a cracked head then it would build pressure almost immediately after starting.
As long as mine runs good, does not smoke, does not loose coolant or oil I think I am going to keep running it. The recently rebuilt 240D does not hold pressure overnight nor does the Honda or E320 (nor any other car I have ever owned). I'm wondering if the cooler temperatures would allow a crack to "open" more - I don't know. Funny thing about it is that the car runs great and the coolant temperature stays between 80 and 90 dC when up to temperature - based on traffic or highway. It does not miss or smoke and I am not loosing coolant.
I have been considering pulling the engine at around 250k miles and going through the top end rebuilding the tranny and replacing all the chain guides at the same time.