Are you absolutly sure you have a bad solenoid? 95% of the time the problem is low voltage going to the solenoid due to high resistance in the safety switches, and ignition switch (which seems to keep getting worse over time). Look for information in this forum from a member named KUBMECH. He very clearly detailed the installation of a John Deere relay kit that costs approx. $20.00. I have a B2400 and struggled for a year and a half with clicking when starting the tractor. The kit solved the problem in 20 minutes! Try to measure the voltage going to the solenoid. If it is less than 8.5 volts, you will have problems, and a new solenoid will not help. The relay will operate as low as 4 volts, and allows 12 volts to go directly to the solenoid.
Good luck,