Finally got it sorted, swapped all my bits onto a mates bike and decided that the sender unit was fubar, £92 later and all`s ok :thumbsup
Checked out the old magnet and thats fine with the new sender (even with a hairline crack) so it may well be up for grabs.... but please remember this item is made of unobtanium and is as rare as Hens teeth...serious enquirees only :bad