E30 Zone

i bought a rear view mirror off ebay for my cab to replace the small stuck on one, however it has like a small spring on it where it would normally go into the frame/roof so doesnt fit..does the cab have a mirror that will fit or do i need to replace the bit near the blank plate is(which i think has the check lights normally)

or just go get a better stick on mirror from halfords?

tia

dave