This is common on mondeo door handles, the reason its sticking is because the return spring has become weak, the only way to fix this problem is to either remove the handle completly and replace or soak the whole handle in a bucket / drum of oil. i had a old bucket of oil sat in my shed and dropped the handle in it by mistake ( well i knocked it off my work bench ) finally found it after a couple of days, gave it a wash down with some GUNK ( bright orange container ( Degreaseing agent )) and it worked just fine.

May work it may not, won't know until you try.

SI.