So - today Ii fitted my Pierberg cam adjuster magnets and had no problems at all. The Pierberg items are absolutely identical to the MB ones that came off - even had the MB part number stamped into the casing. The only difference I could see is the Pierberg adjusters have a stick on ID with their own part number on it. So now I have the oil blocking wiring connectors and new cam magnets so at least should have no problems with oil migrating to parts it should not reach!
I can recommend Parts in Motion who supplied them very quickly with free delivery and its worth looking first for a discount code - I saved 15%.