I would use the o rings as they are fuel resistant. Silicon peels away over time.
I put sillicone on my other 70 series utility 160cc. When I pulled that part and cleaned it with petrol, the sillicone comes right off.
Apart from that starter Irving seal, there is only the bottom seal that is part of the bearing unless I have missed something else? It was pinched when I removed it so it could be the issue.
I don’t see how it could of run on straight fuel as the compression looks fine?