Belly Oil

Is Oil Eater safe for aluminum? I know that the standard Simple Green is not.

Yes "Oil Eater" is fine for the huge majority of aircraft surfaces. I also like it because if you accidentally get it on a clear plastic windshield it won't hurt it. You can wipe off an area if you want then follow it up with just a wet rag. Since it's water based you can dilute it too if you want.

I have tried a variation of the" notch in breather hose" suggestion. I drilled two 3mm hole in the top of my home made catch-can. The catch-can is located at the bottom of the firewall - Minimal, if any effect.

I have a centre belly mount antenna - even a small amount of oil mist is noticeable on the base. Yes both belly & antenna were thouroughly cleaned before the above test.

If the cause of the oil mist is low pressure/vacuum at the oil breather exit;

How would routing the end of the breather exit into wind = posative pressure, go?

OR

Putting a T piece in the breather, with a hose up to the top of the engine bay = higher pressure being introduced to counter negative pressure at the breather exit?

Unable to test T piece idea at this time, however wondering if height of oil tank may also be a factor in oil being ejected out of the breather???

Yes the oil can come out the breather tube if the tank is over filled. 

Yes "Oil Eater" is safe for any of our surfaces. Once you use it and wipe it off then if you want you could follow up with just a wet rag and wipe any residue off. Up to you.