I realize this is a dead post, but my Google search brought me here.
I picked up an L45B from auction recently with the same issue- the machine would not shift into 2nd gear.
For anyone else who might have this problem in the future, the bypass that Treetop was referring to is the following:
In plug X114, 11405 wire is power to solenoid valve Y11. With preselected gear 1: Y11 is ON, gear 2: Y11 is OFF. Cutting this wire should bring back 2nd gear
In plug X116, 11602 should be hot when gear 1 is selected, 11603 should be hot when gear 2 is selected. Confirm this to reassure that the issue is in the controller.
Then, you can take 11602 and connect it to the cut 11405. This will allow 1st gear to be selected and locked again.