my oil pressure switch has leaked, requiring a replacement. Surprisingly, or perhaps not, it is the same oil switch in my 1974 BMW 2002. Same switch, same threads.
How I replace: loosen the oil switch till it is Almost removed. Have the replacement in your other hand. As you remove the old one, quickly insert the new one. If you're quick, you won't lose "any" trans fluid.
Or as you remove the old one, quickly slide your thumb over the hole. Then slide the new switch into position under your thumb.
Cheers,
Carl