BMW E39 failed radiator & failed expansion tank pictorial autopsy, new questions aske

Below I describe an OEM Behr radiator autopsy (verified by date code); and an OEM Behr expansion tank autopsy in a 2002 BMW 525i, with 91K miles on the odometer.

OBSERVATIONS:
- The plastic side panels are held on merely by crimps & a rubber gasket.
- The aluminum of the radiator was in pristine condition.
- There was only a very slight amount of gray gunk in the radiator.
- It was very difficult to find any failure in the plastic side panels.
- An enterprising person could become rich by perfecting a radiator rebuilding procedure that replaces just the two side panels, either with plastic, or aluminum.
- The expansion tank failed at the nipple during removal.
- The Nissens radiator nipple bulb was much larger in diameter than the original Behr (and BMW replacement) radiator nipple (necessitating a larger hose clamp than expected).
- The radiator failed at the nipple during removal (the nipple didn't fail, the radiator tabs failed).
- The expansion tank failed long ago at the bobbing stick rod.
- Cutting the expansion tank in a lengthwise direction revealed inner workings.
- The expansion tank works off of a small disk magnet in the float.
- The float connection to the stick is a very weak point that breaks easily.

HISTORY:
As I was pulling into a parking lot at the mall last week, I noticed a few puffs of steam coming out of the drivers side of my hood. Glancing at the temperature gauge as I idled, I saw the needle shoot to the right from midpoint to about a quarter of an inch to the right of midpoint before I shut the engine down and opened the hood.

I do not remember seeing a "low coolant" warning or any other warning.

I saw liquid spurting from the drivers side, seemingly below the upper hose by a couple of inches, and of to the side, as if a seam split. When it cooled I filled the radiator with tap water and bought a few jugs of water at the mall to keep in the front seat, just in case.

I unlocked the cluster, by memory, with a few mis-attempts. The procedure was basically the following:
- Press the right cluster button for about ten seconds
- When the first test showed, press the left cluster button
- This shows the VIN last seven digits (IIRC)
- Add up the last five digits of my VIN (e.g., 30)
- Press the right cluster button until it showed the last test (LOCK ON)
- Press the left cluster button until it showed the VIN sum (30)
- Press the right cluster button
- This should unlock the cluster
- Now press the right cluster button to go to test number 07.
- This reads out the coolant in degrees centigrade.

At no point in the 15 miles home did the temperature go above 93°C.

Once home, I proceeded to replace the entire cooling system, using parts previously stockpiled from OemBimmerparts' web site after my previous alternator and belt drive system emergency overhaul.
- One users' example of alternator failure (AAA emergency tow) (1) (2)

Below I will describe, pictorially, the radiator and expansion tank (aka surge tank) autopsy.

One observation worthy of note is that it should be possible to "rebuild" a radiator at vastly less expense merely by perfecting a method of re-crimping the side plastic panels.

Even better would be a method of crimping on stamped aluminum panels in place of the side plastic panels!