I do not have so much experience with the Libelles, but things I remember:
- As with all Glasflügels: Check if the connection between the main pins and the wing spar stubs is okay (http://streifly.de/TM201-31.pdf). Repair needs a professional workshop
- check the ailerons for excessive play. That's a quite common issue with the Libelles. In many cases, a fix requires sending the aileron drives to Streifeneder
- check for play in the lift pins. This cannot be removed with washers as with the F, but the pins will have to be replaced
- check the air brake drive for free movement
- check the elevator drive for play and any hidden cracks
- check if all the AD have been taken care of

Best,
Christoph