The loose seat is permanently fixed and can be modified for 1 hour of your time and made more comfortable to sit in with the seat tilt modific for $45. The bad seat bushings are a problem on every Z3 and nothing to worry about. The. Fix can be bought here.
The seat bushings alone is here.
As for the price, I think you are closer with the 9 thousand than the 12 but if they do the inspection II, you would do just fine at 10,500. The low miles are a huge plus but the automatic transmission brings the value of the car down a bit. IIRC, it is a 4 speed, not the 5 speed that came out a little later.
1999 Boston Green M Coupe
2002 Z3 2.5 Automatic Roadster
2013 Ram 3500 Crew Cab Dually, 850 ft/lbs torque, stock and staying that way
1995 318i spray paint red, 170,000 miles and climbing