With trans in cat. While taking apart my valve body and stater plate for repair. I had a small square piece of steel fall into my drain pan. I have no idea where it goes. I do no see anywhere in my service manual that it would go PLEASE HELP IF YOU CAN. Measures 1 1/4 square.
It looks like the reverse brake band operating strut. It goes between the reverse band and the reverse band operating lever. Buick part no is 1333465.
From the chassis service manual, it appears in Fig 5-16 (end view). A better view appears in Fig 5-35 under the instructions of how to catch it during disassembly. Assembly instructions are shown on page 5-63.
Once the strut is in place, the grip on it is very delicate until the servo body and operating pin are in place to hold it securely. See the caution note about not moving the reverse band operating lever or else the strut will fall out. If the strut was out of place while driving recently, the reverse gear would be inoperative.
There are two similar struts (with a different part no) used on the low band to engage low gear. Would be a good idea to check position of those as well.
This vendor site confirms the dimensions of the reverse strut: