Kempoguy

Yes, leak was around the bottom of the expansion tank, but couldn't pin-point it exactly. Pour water in the top, it came straight out somewhere near the bottom

Yes, #4 seems to be the jobbie. The e46 has the problem - the coolant fell out all over the road and leaks like a sieve when refilled. I pulled to expansion tank out expecting to find a hose or hose clip problem, and found this - I dunno if it's the root cause of the leak, but I'm sure it isn't helping any. Any idea where to get one?

Nah - definitely out of the coolant expansion tank - right at the bottom. If I pulled the trans apart, I'd be deeply in the sh*t and so out of my depth, I'd have a divorce on my hands

Hey , I'm new here. I have been chasing a leak in/around the coolant expansion tank - removed the tank and at the bottom found the bits in the attached photos. The black fitting has broken - one of the bayonet clips has come off. Although this may not be the cause of the leak, I am sure it's not going to help either. What I need to know is: 1. What is all this? I'm guessing it's some kind of pressure valve. 2. How does it actually fit together? It all came out in pieces when I removed the tank. 3. What parts do I order? Or, where can I find out what parts to order? Appreciate any assistance you may offer. Cheers