I suggest you read your warranty to see if the wiper transmission is covered. They will usually specify 'motor only', or indicate the 'motor assembly', which would include the transmission.
Friend of mine had a Thunderbird that developed a tranny problem that turned out to be a bad sensor. The dealer said sensors were not covered, just mechanicals, and billed him $1200. Warranty stated specifically 'hard parts, gears, housing, and sensors'. Dealer finally caved.
