240 - rebuilding upgraded 15/16" master cylinder - question

[DAT240]

My 240 project continues - makes the lockdown easy. I'm upgrading the brakes to Toyota 4x4, changing the master cylinder to 15/16" (thanks for the tip Laverne and others). I sourced a used master, bought a rebuild kit which was tougher to find than I expected. I saw a post elsewhere that advised not installing a small rubber piece in the front brake fitting on the master - referred to as a "duckbill". See photo (the picture with the calliper is just showing off - sorry). Anyone familiar with this who can advise? BTW - my unheated garage is not helping to speed this work along at all.

Datsun 15:16 master.JPG

Datsun Toy calipers CR coilover.JPG

[DAT240]

Thanks Laverne - I'll keep the rubber duckbills - font of knowledge as usual!