If you're satisfied that only the "ceramic encased magnet with electrical connection" (which is a good description of a speed sensor) is bad and that the compressor rotates normally and has not had any problems except this, I'd replace the speed sensor and give it a try. If you call either of these two places for the part as they have proven very helpful to me in the past.
http://www.ackits.com/
http://www.acsource.com/
I know that you're not planning a full reseal, but this is worth reading also:
http://www.pelicanparts.com/techarticles/911_Nippondenso_rebuild/911_Nippondenso_rebuild.htm