Just cleaned my engine bay (only bought this'85 gsl last month), and noticed that the rear rotor housing has the "12A MAZDA" logo stamped into the aluminum. I'm quite sure that only the front housing had this stamp on the other three 1st gens I've owned (an '81 and two '82's).
Unless Mazda changed this on '83 and later 12A's, this engine must have been rebuilt at one time and had the rear housing replaced with one that used to be a front housing.
The car is originally from California, showing 125,000 miles on the clock. Being a cynical bastard, I find that difficult to believe, especially if this really is a rebuilt. But ompression was 120 psi on both rotors during the pre-purchase inspection, and overall condition was very good so I bought it anyway.
Does anybody know if Mazda ever sold the 12A with this stamp on both the front and rear housing?

 

ALL rotor housings have a marking of some kind in that spot, they just look different in different years/models.