Brian
I would not be too concerned re the fault codes
They have been generated since the last time a Dealer cleared faults and only you know the last time the bike was with a Dealer, you have a reasonably high no of Kms on it, overall very few faults have been logged and none are currently present plus none show high No's of occurrence
41705 Fuel Level Indicator, could have been caused by turning on ignition with the sensor disconnected ?, it is only a "lever" type ie a switch
37641 KL30 under voltage, bike had a low battery voltage when ignition turned on at some point
37642 Implausible Photocell voltage, not sure what they are referring to with "Photocell", implausible means not in expected value range
Jughead or another person more familiar with the 2006 1200GS would be able to shine more light on it