[hatzie]

Download the four early GM T400 parts books from the link in my signature.
The paper T400 parts and illustration catalogs ended in 1993.
The wiper parts pages in the Illustration Books are as follows;

1. 1988-1991 Illustrations on PDF pages 678 & 679.
2. 1992-1993 Illustrations on PDF pages 1114 & 1115.

The LH & RH transmission assemblies are listed as the same part numbers from 1988-1993.

I'm surprised the ball and socket joints don't have some kind of nylon wear sleeve under the bolt-on caps.

You'll find several wiper motors are listed with almost yearly part number differences.

The rotating arm with the machined balls that mate with the transmission arms is not listed separately from the motors. I'm not sure whether the clocking position on the rotating arm will be the same from year to year. This may be the difference or it may be something else.

Hope this helps.