I have a late 80's 50mm/1.4 which was made in Japan. I thoroughly enjoy shooting with it because it is fast, solid, very well constructed and produces fine results. The problem is that over the years the threaded portion which accepts filters et al has been damaged and 40% of the threaded portion is missing. Have been living with the lens 'as is' for quite awhile but every now and again I get into a situation where a filter would make shooting easier. I would like to know if I am facing a easy, quick repair job or if major surgery will be required. Thanks.