here is some proof about the older mag. cases

http://www.burningart.com/meico/valhalla/mag.html

as far as What i have heard--the heads of the 2.1 wasser boxer have a high
mag content--hence making them soft. one of the reasons that they pit so
easily and eventually leak. i've had more than one mechanic tell me that a
head actually becomes porous with age and will be leaking combustion gases
through the head into your coolant--all because of the high mag content.

this is all hearsay though. i just know for a fact that the air cooled cases
had high mag content--haha--i might be one of those bad crowd VW guys--haha.
but the burn is quite spectacular