2002 Vauxhall Corsa oil pressure switch

Hi, i have had problems with this before seems a common fault, previously io have just changed it for a small fee but this time i noticed the bolt was loose so i tried to tighten but to no avil it just kept spinning so i bought a new one but agin this just keeps spinning, are the threads knackered?? ive had PTFE tape on it but again this doesnt seemed to have worked. Is this likely to be a major problem??

thanks for your help