A833 real seal and reverse indicator switch

Hi all, I recently picked up a 1975 Duster that was orginally a slant 6 auto. It's been through a number of owners and over the years it has become a 383 magnum, 4 speed. I've begun going through it and some of the many issues it has includes a leaking rear seal on the trans and a leaking o-ring (I believe) from the reverse light signal sender. My questions are 1.) Do all A833 4 speeds have the same rear seal size and type? The markings on mine show C 99129M (cast into the trans) and a stamped number of PT6355037CP. My novice decoding of the cast in numbers indicates this was used from 1969 - 1971. And 2.) what is the proper description of the reverse signal sender so I can look it up to order a replacement. Any further advice on the replacement of these two items is always appreciated. TIA