Quick question, I noticed a hole on the rubber boot. Anyone with knowledge about these Master Cylinders know if this is normal? Looks like a hole to relieve air. Just want to double check before installing, thanks.
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I've seen this on other brands or they at least have a groove / hole at the end of the master cylinder. ( hole pointing down. )

If the last seal in the MC leaks brake fluid, these holes let it leak out signaling a problem.

That makes sense

Hole goes down. Weep hole to let you know you have a problem.

Actually it points to the side not down.

I think I am just making too much of a big deal out of this

Basically it is a breather for the bellows as they are tight fit on the rod and cylinder ...just not an issue go well you will be fine .

That's what I was thinking, too. The fluid will find its way out one way or another.

think the OP found that out already with his old one .

It's for air
The cylinder should not leak here ................... wait for it .................................
Unless it's a URO and it will pump all your fluid out this hole providing no braking whatsoever

I'd assume that it's there to just provide release for air, but having brake fluid coming out would definitely tell you it's time for a new one.

Quick update:

E-Mailed ATE and a german guy told me the hole is normal (he said 1.5mm). The hole is for air to release during operation and should be pointed down.

For those who said it was for air good job

If it leaks you don't know it until your brakes go bad or you notice the MC level is low. You really can't see the fluid leaking on the floor until it get catastrophic, the pedal board is in the way.