rokami,
There are two different issues in your post;
Firstly UL91 is not Mogas and is approved without any additional procedures or restrictions as an alternative fuel to 100LL in the Cabri G2 . This is confirmed in Guimbal Service Letter SL 13-001 A, see quote below.
- Unleaded AVGAS UL91, designed to replace AVGAS 100 LL in Europe, can
be used with complete interchangeability.
The same service letter also approves the use of Mogas in the Cabri subject to certain conditions, see extract below
- Unleaded automotive gasoline is approved as an alternate fuel, under
conditions of supply that are commented hereafter, and by respecting additional limitations that have low impact on practical use
I regularly use UL91 in my Cabri.