Several years ago, I saw a documentory about this raid. So I assumed it was an open secret. Didn't Mossad see the doc?

In this paragraph below(copied from the article) 'transparent' suggests the opposite of what you intend to say. The word should be 'invisible'

Suleiman instructed his people to avoid transmitting any message in electromagnetic ways, and to exclusively use physical copies. He established an organizational system which remained completely transparent to the Israeli intelligence for many years, despite the huge resources Israel invested in Syria to ensure that nothing important escaped its eyes, and mainly its ears.