If I remember correctly,... 17mm is a little tight for the second hole...
I would reuse the old gasket,(just wipe it clean) and install on the first hole...
Give 4 or 5k miles, or until you start hearing chain noise, then pull it again to go to the second hole with the new gasket...
19 or 20mm, and you can go second hole...
Nice thing?,... your adjuster can't fall out now, thanks to the pin...
...
If you have time,... Versy or Dave can confirm, but that's what I remember...
Betcha' feel a lot safer now...