brake fluid question

[car10002]

Hi

Have question, what would cause a bit of brake fluid to come out the container on a new master cyl between the container and metal part on master cyl at the o rings or the lid in the ba.

Opened lid on container and it hasn’t lost any and level hasn’t done down.

Had a whole new master cylinder fitted a few weeks ago and everything checked out good.
It doesn’t do it all time, just some.

Is there any chance that it might just be spillage and just a bit full.

Fluid is at max

brakes still work ok

Thanks