I recently upgraded my twin cam 96" to a 103" with a S.E. 103" big bore kit with the S.E. 255 cams and the stage 1 S.E. breather & filter. The engine's been doing fine, it's done broke in as I've rode over 6,000 miles since the upgrade.
The issue from day one has been oil leaking onto the top of the engine right above the cam cover, first I replaced the 4 little o'rings, 2 on the banjo bolts, & 2 on the S.E. backplate where it bolts to the heads, and I also replaced the gasket between the throttle body and the S.E. backplate, IT'S STILL LEAKING. This weekend I took the football cover off, then I took the 3 torque bolts that hold the filter, and there it was all that oil between the backplate and the air filter, the air filter had some oil inside but not much, instead from where the vent holes come out on the backplate its dripping straight down the backplate and then between the backplate and air filter onto the top of the motor, and I'm not aware of there being a gasket between the air filter and the backplate, I can clean it good, go on a good 30 to 50 mile ride, get back, look, and there's the oil on top of the engine again, not a lot but enough that you can tell it's there and more towards the back where the jugs are rather than towards the cam cover, it's getting frustrating.

 

I don't think you can get oil into / onto the air filter assembly from anywhere but the two vents. I would suggest dropping the oil level in the engine back 1/2 quart and see how that works.

 

It is coming out the vent holes (with circles in the pic) and then dripping down the backplate (where arrows are drawn) and getting between the back of the air filter and the backplate and dripping on top of the engine just below it. I never add more than 3 & 1/2 quarts at oil & filter change which I do myself, right now on a hot check on the jiffy stand it's at the halfway point between the low and full marks.

 

It's not "leaking" so to speak.

Your pic shows how the A/C is supposed to handle blow-by crank case gases.

The o-rings and the banjo bolts are the pathway the crankcase gases use from the umbrella valves in the heads, to the air cleaner. The blow-by enters the air cleaner area in the spots you have circled in your pic, and then gets sucked into the throttle body to be burned in the combustion cycle.

As some have mentioned, keeping the oil lower than full will reduce the problem on some bikes... The crankcase fumes frequently contain a fine oil mist.... something is not right with your install if that much oil is being pumped/sucked into the air cleaner.. You seem to have a bigger problem than most. Since it started with the big bore install, I'm guessing you have a problem.

I have 3 twin cams, one w/stage III, one with Stage II, and one with Stage I. None have had oil dripping from the air cleaner area..... I do not consider oil dripping from the air cleaner as normal... a little oil residue inside the air cleaner and on the air filter between services, yes.... oil dripping, no.

Assuming that the umbrella valves in the heads were not touched, that the valves were not touched, and that the excessive blow-by wasn't happening before the big bore kit install... I'm gonna guess you could have a ring install issue.

A leak down test will let you know if you have a ring install issue...

Good luck tracking it down.....

 

I installed the discrete oil breather kit on my "13 RGU, have to drill and tap a couple of holes for the hose barbs, routed the hoses down to the front of the bike away from tires and brakes. Got my kit from DK Customs. Suggest getting the tap and drill kit also.

 

Search this forum for breather bypass. Many of us have the same problem and have found several different solutions.
Like senior mentioned, DK Customs is a good place to start.