t20 tiger cub breathing

I have just finished recommissioning a 63 T20. The weather has been such crap that I have not had the chance to ride it yet but it starts and sounds good. I does seem to be passing some oil out of the engine into the primary. I am wondering what is used to vent the crankcase on these bikes. Can anyone explain the breathing system? I am not even sure if the breathing is intended to be through the primary like many older bikes (e.g. velo mac) or if there is another form of breathing.

Thanks in advance for any input.

I can’t recall the standard breather arrangement. But I do know that when I built one as a yoof, managed to build it with NO engine breathing facility at all !

I realised after several attempts at sealing various leak, with yet more silicone, that sumthin wasn’t right !

I put a big open breather from the old distributor drive plug, looked kinda RE Continental GT to my youthful eye and it did work instantly currying about 50 leaks !

Yours is a ‘63 so doesn’t have a distributor I assume, so this option would be open to you as well if you can’t figure out the original method.