Hi Twinglish.
I’m not familiar with the Brinks version of the disk lock but I have experience with a few other models.
They vary in quality. The Master version will generally open fairly quickly with the “good ole snake”. The Abus version will pop open in fright if you give it a dirty look.
For a quality version like the Lockwood and I assume the Brinks you will need a short hook and a bit (lot ?) of practice.
I had several Lockwoods that I spent many hours – stretching over a couple of years – trying to open. In desperation I sent one off to Oldfast and he opened it. Just knowing that it could be done was a big boost and after a few more attempts I got it. Then proceeded to open the rest.
I can now do them no problem but they are not easy.
In summary. If it is a good quality cylinder, made to tight tolerances, you will need a short hook
and SPP it.
Don’t give up. If you can’t get it. Put it away for a week or two and come back to it.
Eventually you’ll get it and OH what a feeling.....
PS can you post a bigger photo of the Brinks?