To answer my own question.... I called Lewmar who sells a direct replacement for the old Simpson Lawrence 900, and who still has some parts for the old S-L windlasses. The purpose of the one-way or clutch needle bearing is to stop the anchor and chain from dropping once you take your finger off the "Up" power button.
You can also buy the individual bearings from a decent bearing supply source. Based on what I found when I took our S-L 900 apart I don't think a failure of the one-way bearing would have caused the windlass to have stopped working. The main needle roller bearing where the gypsy shaft comes through the gear box housing had totally seized. When I was taking the windlass apart I didn't realized that there was a roller bearing there as it was in such bad shape. In spite of that bearing failure the windlass had continued to work, and the general windlass construction was robust enough that nothing else broke.
I am replacing 2 failed bearings and the main shaft seal, and having new brushes fabricated for a total rebuild cost of somewhere around $100.