Here is a photo of one of the main culprits for coolant leaks.
Yes it's the radiator bleed.
The problem s usually stem from this being overtightened after bleeding air from the radiator.
What you have is a threaded plastic bolt tightening into the plastic radiator casing. Easily overtightened and then it will leak.
The area that the bolt screws into is only 5mm thick meaning that the actual number of threads holding this crucial bolt in is only about 3-4 threads. Overtorque even slightly and OOPS!
I've been thinking of ways to eliminate this weak point in the cooling system and came up with two ideas.
1/. Use a metal 'Rivnut' and bolt to replace the plastic.
This is what I'm talking about.
Now there are two different ally rads available with different thread sized apertures.
Mine has an M12 thread and an M8 Rivnut is a pretty good fit for this size.
As I didn't intend this to be my final solution, I wrapped the rivnut in PTFE tape before inserting it and tightening it with the applicator. Otherwise I would have coated the outside surface of the rivnut with an appropriate epoxy adhesive
Then an 8mm Stainless Steel bolt with an appropriately sized 'O' ring fits the rivnut.