Here are some thoughts:
* There are two very different kinds of seats for the K1200/1300GT.
The "early" type of seat was made for model years 2006 and the first half of 2007. These early seats were manufactured through December 2006 (which was sold as the first half of the "2007" K1200GT model year).
The "late" type of seat was made for the 2nd half of 2007 model production and was included with all of the K1300GTs. Manufacturing of the "late" seat type started in January 2007.
* Each seat type comes as a matched set (rider and passenger). The rider and passenger seat must be the same type or you cannot fit them together. You cannot mix an "early" type 2006 rider seat with a "late" type 2008 passenger seat or visa versa.
* The "early" seats have a single wide tongue that goes from the passenger seat into a slot in the rider seat.
* The "late" seats have two tongues on the outside of the passenger seat that insert into two slots on the outside of the rider seat.
* Here is an image of the two types of K1200/1300GT seats:
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I have the "late" seat on my 2nd half 2007 K1200GT. It was built in April 2007. On my "late" type seat, the passenger seat has two tongues on the front outside edges that fit into slots on the rider's seat. I have discovered that it is possible to fit the passenger seat into the rider seat incorrectly. Everything locks down, but they don't feel right, and the seat feels "wiggly." When the seat is improperly installed that way, you can lift up on the front corners of the passenger seat and they come up more than they should.
Here is how I make sure my "late" seats are properly fit into place:
1. Insert the front rider seat under the tank. It should be obvious from tank paint fading or dirt or whatever that it is in the correct position.
2. Press down on the back of the rider seat so that the two round rubber/plastic pegs are fully inserted into their respective holes on the motorcycle. At this point, the rider seat should not wiggle provided that you do not lift it.
3. Insert the passenger seat tongues under the riders seat. When both tongues are properly inserted, you should not be able to lift either side of the front of the passenger seat when you press down on the rear of the rider seat (to keep it in place). If you can lift the front of the passenger seat after the tongues are inserted, then you probably inserted the tongues too high behind the rider seat. Try again.
4. Push down on the back of the passenger seat until the latch engages. The seats should be locked in place. You may check the front of the passenger seat again to make sure it does not lift or wiggle.
That was for my "second type" K1200GT seat (late 2007 and beyond).
If Steve's K1200GT has the "early" seats, then I wonder whether the tongue is fully engaged.