Bill -
I had a VERY similar situation. My Sears riding mower had a defect with the deck. I enjoy taking things apart so I toyed with it. I removed the deck, made every possible adjustment and still had problems. Luckily I had the service plan.
The tech came out and smiled, "I know what it needs" ...and proceeded to do what I had already tried. I mentioned it to him, but I can understand that being his line of work, he went through the motions anyway. Didn't work.
He ordered some parts, 1 week later, parts show up....I toyed with the parts and realized they weren't going to solve the problem. I make the appointment with the tech, he shows up...I explain why I don't think they're going to work....soooo....he orders some different parts.....parts come, I check to see if they're going to fix it...NOPE!!!
Tech shows up again, I explain how I don't think this is going to work either.....he agrees and decides to call for support.
I call the Service line and explain what's happening. They thank me for my continued patience.....I ask them how long do I have to go without a lawn mower, and who is going to pay the landscaper bill that's been accumulating while my mower has been down. The representative informs me that as long as I gave the technician a chance (1), I can request a replacement.
Right there and then, I said "I WANT IT REPLACED"!!!
NO headaches at all....aside from waiting for one to be delivered. (Yes, I had them throw in the delivery as well)
Bill, with it being snow season, I'd bitch about it and demand a replacement for customer satisfaction reasons. You've already given them ample time to get this repaired. It's now within your authority to request a replacement. Play the words in your favor, and they will not give you any grief.
Good Luck -