Berlingo E500 SA18 Motor Cooling

January 2013 54000 miles total an unlucky year?
Two further disasters to report i'm afraid.
In January coming off the M4 the motor suddenly made a nasty rasping sound.
There was snow on the ground. I had just enough momentum to coast off the M4 onto the slip road verge.
I removed the motor inspection cover and noticed bits of graphite brush crumbled up on the cover.
I called the AA for a tow home.
The Motor was removed and connected to 12V car battery. It turned in 90 degree jumps.
The armature was removed and replaced with a spare.
Again the 12V battery was connected. The motor turned smoothly...
I could see no sign of damage to the original armature which had lasted 30000 miles, but on closer examination there were tiny beads of copper and a small hole in the banding near the commutator.
Two of the armature wingdings have welded together near the commutator causing this peculiar fault..
The repaired motor only lasted a week when I thought I could smell burning. I dismissed this at first as some bonfire smoke I had just driven through, but when I stopped the smoke cloud came out the front of the van! The field winding had burnt out!
This also badly damaged the field speed controller.
I removed the motor again and put the original Berlingo motor field back. Now the van has the original motor and speed controller back.
Possible causes of SA18 burnout
1) Cold wet weather. water getting into motor???
2) Motor over-heating or temperature fluctuating when going from motorway driving to rest - expansion and contraction damaging winding insulation enamel - I've noticed its flaking off the armature flat wire.

Motor Cooling
A breakthrough! Traction motor cooling is provided by a weedy little 12V centrifugal blower running at 3A about 500 RPM there is insufficient cooling air from this to cool the motor at high power (driving on a motorway) The traction motor will rapidly overheat and burn out.
I tried putting 12V directly on the fan motor but at first smoke came out! It will draw 40A at 12V until the mess of old oil and carbon has burnt away. However after a few minutes running at 12V the motor speed picks up to 3000 RPM and the smoke stops. The current drawn drops to 10A. This is how the motor is now connected there have been no further overheating problems, the traction motor is already damaged but hopefully this will extend its life a bit...I will let you know.