fixed mine with a SpeedoDRD
I figured mine was off about 10%, so picked up a SpeedoDRD. Very easy to install and operate, and cheaper than a Speedohealer.
When I installed the DRD, the correction was -6.6%, but that's according to its own calculations. I didn't check to see if it changed from stock, to after the install of the SpeedoDRD prior to inputting the correction.
None the less it's somewhere between 6 and 10%.
My question is, who wants to do 90mph to test their speedo? Wouldn't an average top speed of 65mph be adequate? Fwiw, I dialed my speedometer in at 100kph... any error above or below that is negligible or moot.