Heading your advice, I visited a well established, independent Transmission Shop in our city. They are in this business since 1959. I showed them your (printed out) response/advice and they agreed to a letter with your comment. The owner personaly done the diagnostics. He plugged in the code reader and vent with me for 10km test drive. (With the code reader plugged in). He was explaining to me all that time what the code reader indicated.
First of all, he checked the fluid and level. The colour was all right, BUT
THE LEVEL was too low according to him. The level should be a one litr more than the GM reccomends to car owners. That is why (he said) the solenoid failed.
He further said that not many people know that and GM will not change their instructions to car owners, since it would create a tsunami of law suits and forced possible recalls.
Anyway, my car will go into their shop on Friday. It is 4 hours labour (according to him) and 80 bucks (Canadian of course) for the part - solenoid. The total cost = $375.00 Canadian.
Once again he agreed with what Bnaylor 3400 said here.
Thank you again!