First, accept that you have a little too much in there. It will have to vent out. Also, as it expands with heat, you will get some more venting oil.
I put an empty plastic jar over it for a while to keep me or others from getting an oil bath.
Also, Some of your problem is air. It will eventually settle out.
Now, the design issue with the original vent is this, straight pipe, hole at top. Burp... You get a shower.
I made an expansion chamber that allowed the oil to drain back in. Also, I made my hole on the side away from me and put a rubber
Here is a rough cutaway drawing
Black is close to OEM, orange is 1/2" to 1" adapter, bored out to just slide over pipe and welded on, red is 1" union, green is 1" cap with an internal dome, blue are holes.
And here is what it looks like on the machine.
Doesn't solve the oil loss if over full, but it seems to handle expansion better and if it does burp, I don't get a shower.