Shimano doesn't sell the tool to remove the proprietary 4 point jam nut on these brakes, and no one sells the tool. However, if you file out the 2 points between each of four on any typical 12mm box spanner wrench, you can make your own tool and take these apart. If your brake is seized up, the issue is due to the main bolt(s) bushings. They are made from a mild steel sleeve with a thin plastic liner that the bolt passes through. Use a knife to remove the plastic sleeve. The brake will still work fine without it. Grease the sleeve but not the thrust bearing. Also press out the assembly using the body of each arm. Do not pry or touch the outer thrust bearing area. The thrust bearing on the end does not do much at all. It has a bearing shield and basket built in. This is all integrated into what you see from the outside. If you pry on this, it will break. The thrust bearing has 2 steel hardened races that look like washers. The assembly should be cleaned but kept dry without lube. The bearings will easily fall out at the worst possible time so be aware and keep the assembly confined where the balls can't run far.
After modifying and initially servicing this brake, it has lasted almost 2 years and is still going. It needs cleaning and (re)service close to every chain lifetime. I have serviced it 6 times. It is beginning to need replacement, but that is 2 years of life extension for a hardcore daily roadie living in a salt water environment.
(First post here to get started. It is just a carry over resource image I had available)
