Unfortunately the Hall Sensor by itself is no longer available as a separate unit, you have to buy the whole distributor, about $190 ~ 210, anything higher and you are getting ripped. A few years ago you were able buy a kit for about $40. I searched all over but couldn't find one for my '91 1CQ but you might be more lucky with an 87. If buying a rebuild, make sure it is done by Bosch. I was fortunate enough to pick one up at my local junkyard for $35. This unit already had the sensor replaced. Changing the sensor is a bit of a PITA, biggest problem is grinding the rivet head and driving out the pin.
Just for reference I found that Siemens HKZ101 or HKZ101S works in place of the Bosch sensor in the 89 - 91 Distributors, might also work with others. My distributor came with the Siemens sensor and that is what I still have under the hood.
HME also makes a replacement for the Siemens but I was never able to find one. If you do a Google search for the Siemens HKZ101 you find a wealth of information.
