Thank you all for input .The plastic item was on the bottom of the door doing nothing .So i have fitted the new door check strap not merc one but aftermarket that came with a nice cover on it to keep water out and lub in ..I gave it a good drink of oil and mollyslip,well i put molly on with a brush,and fitted the cover back on.Offerd it up to the door from inside .Would not fit with the cover on .The thing stopping it going flush was the rib in the door ,so i cut the bottom corner of the plastic cover of the check strap this fixed it Another thing i came across is the deadening sticky pads had come away from the inside of the door , realy worth checking out on the older cars as if it falls off, it can and will jam up the works.Refitting the door card was a pain it just would not go on the door .Reason was i had put tape over one hole that the door card hook goes in to, silly billy.