I've been looking for an AM filter for my IC-756 for many years, and just stumbled across a filter from W2ENY. I think he used to offer these, and went out of production for some number of years. He has brought a limited number of these back for sale. I emailed him, he replied almost immediately that he still had some, and I ordered one. I'm happy to have finally found one of these babies. I work AM from time to time on 160 thru 10, and usually operate one of my boatanchors due to the w-i-d-e passband on AM. His page is:
http://w2eny.com/6kc_filter/ I received the 6khz AM filter from W2ENY for my IC-756. The instructions were EASY to follow and the mod was quick and simple. I LOVE it! I've been working AM on 80, 40, and 15m with the 756 and have great selectivity on AM. I replaced the 15khz filter in the 455khz I.F., and have noticed no issues with working FM on 10m, listening to broadcast stations, etc. My 18 year old IC-756 is now perfect in my opinion, and everything is working great. This is the filter the rig should have come with from the factory, as all modes are well behaved, now.
UPDATE: 3/16/14... After using the filter for about a year, I felt the need to make another change. The instructions from W2ENY mentioned to replace the 15khz filter in the 455khz I.F. with the 6khz AM filter. I found, when operating AM on 10m, it is desirable to have access to the 15khz filter to open up