Sorry I've taken so long to rely. I filled the transmission with transmission fluid; then, I used long handled pliers on the transmission arm at the transmission. I slowly worked the arm back and forth. After about five minutes I began to get some movement. Eventually I could move the arm easily back and forth (forward to reverse). Then I went on deck
and tried shifting at the helm
. All was well. In the spring I will drain the excess transmission fluid from the transmission. The final test will be with the boat in the water. Thanks again to all who made suggestions.