As for a 9dB difference, the usual reason for L/R level difference is the linearity of the input and output potentiometers…. they are never perfect and when new they are often as much as 1dB adrift at certain parts of the scale. However, a 9dB difference is virtually impossible and I would look elsewhere for the reason. The most likely cause is an incorrect connection on the input…. For balanced connections 2 is +ve, 3 is -ve and 1 is ground. All must be connected. For unbalanced connection 2 is hot and both 3 and 1 must be grounded…… if pin 3 is left hanging then the level will be at least 6dB low.
So check both input and output connections!
On the earlier V1.05 versions, we sometimes had problems with the output stage going ‘one legged’, but the later V1.07 versions did not suffer from this.
If there is a real electronic fault, I’m happy to let you have the circuit information for that model, or if you would like me to fix it, the deal is that I charge US$50 plus the cost of returning it to you. (I’m assuming you are in the US.)
BTW, when sending equipment to me for fixing, be sure to give it a low value for customs….. the risk of getting it impounded is much higher than the risk of losing it; a $25 valuation ensures it gets here without problems!