96 e300 heater pipe broken. Cause?
 

Well I figured out why the heater hose kept popping off on the engine side of the heater pipe going through the firewall on the US driver's side. It looks like the last half inch or so is broken off. It is a very clean break. Almost like it is sawed. The car has a 176000 miles.

Is this normal wear, too much green anti freeze, bad mechanical work or other defective part or blockage in the heater loop or possibly any of the above? My guess is probably a combination of a few of these things but looking for any ideas and experience with this issue on the forum.

I've temporarily patched it up with a new clamp and some gasket sealant until I can order a new heater pipe from the dealer or on pelican parts