Hi ive got a 2001 mondeo petrol duratec good compression but uses oil more noticable when driving car down a hill whilst foot off throttle and then when u hit throttle a puff of smoke out the back but then clears..spark plugs are ok not oily,ive been told poss valve stem seals gone but if replaced they tend to smoke more after is this true or is it worth forking out to get done and what about valve guides??

Not a cheap job to do the stem seals.
Your head would need to come off and checked by a professional.
Stem seals are not an amateur fix I'm afraid.