Until I read "85mm f1.4" I was all set to recommend a tube of silicone grease and a cocktail stick to spread it on the focusing helicoil.

Unless you're reasonably skilled as a mechanic I'd get it dealt with by a pro. I re-greased a 55mm 1.8 today but that was a case of repairing a fairly common lens which I'd paid very little for (the tube of grease cost almost as much as I paid for the lens!) Worth the effort though as the optics are utterly superb.