Brake Fluid.
The '96 to '05 versions say "Use Dot 5 fluid" on the master cylinder cap. The 06 version says "Use Dot 4 fluid" on the cap. That's the only difference.
You should be able to buy a chrome '06 master cylinder cap separately to fix this. Do NOT put Dot 5 in your system, without first getting a rebuild kit for your front caliper. Of course, then you'd have 5 in the front, and 4 in the back brake system.
I would not use the Dot 5 cap, and then use Dot 4, too confusing for others.
This switch to Dot 4 is a real beef I have with the MoCo. Dot 5 has been fine for years, and now to try and win back some of the cop bike business they lost to other manufacturers who offer anti-lock brakes, they have switched to Dot 4 for ALL the bikes. Buffoonery if you ask me.