Just wondering what is the purpose of this extra breather.

Its a crankcase breather in the primary gearcase above the drop gears. It doesn't go into the dry clutch area. Mainly used on 1100S style solid blocks because there is no tappet cover breather. Later engines also used a breather on the timing chain cover.

As Brad has mentioned, in Australia it was originally used on Morris 1100S with a PCV system as the only crankcase breather. If you are running a PCV or CCV system it’s really good at removing the crankcase fumes, but if you run the breathers to the air filter or have them open you might need more than one breather port

I used that type for a few reasons
The transfer case was drilled and open already (it can also come blanked off)
I was planning on running an “ultimate engine steady” that meant I’d have to remove the side cover breather.
This breather connects to the bottom of the crankcase (under the pistons) and I figured it’d be good to have one upper and one lower to remove the fumes
I also have some rocker covers without breathers so an extra breather is needed then

And feel free to reply to the initial thread with any questions

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I used to use the flywheel housing breather on my 1100S block to a PCV valve, but have moved it to the alloy rocker cover.
Reason - at high rpm on tight long LH bends, the primary gear threw oil up it, making like JB 007.
Working well.
If doing this, ensure it's not directly above a rocker as that can throw oil up it too.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.