Mini Cooper S Paceman dyi car keys fob fix

Hi, i am the owner of a mini - mini paceman to be precise.
Unfortunately a few weeks ago the key fob (round part) detached from the actual key without me noticing whilst i was crossing a road; once i realised i had lost one part of my key i traced my steps back and i was lucky enough to be able to find it in the middle of the street.
Few cars had run over it but for 2 weeks after this happened all 3 lock/unlock buttons were working just fine. One by one then slowly stopped working over the course of week number 3.
Before buying a new key from mini (for £160) i was wondering if there could be a diy way to fix it.
Can you help? or do you know of any other mini blogs where i could seek help?
many thanks in advance for your help.