The rockerbox (as well as cam chest) breather is connected to the oil tank breather. ¹⁾
If you blow down the oil tank line…air comes out the rockerbox vents (or cam breather hose).
There are airways linking these compartments together and in looking at these airways.
If one pressurizes, they all pressurize. So breathing the sportster engine needs an overall approach.

• Pushrods connect the rockerbox to cam gear case. Air can pass.
• The rockerbox oil return connects to cam gear case. Air can pass.
• The pinion gear shaft is hollow and connects the crankcase to the gearcase (but would only pass air with the engine off).
• Airways thru the wall joins the sump and the scavenge side of pump.
  • Piston downforce pumps air and oil from the sump to the gearcase compartment.
  • This would equalise air pressures in the two chambers.

86-90 engine breathing paths. 2)	91 engine breathing paths. 3)

92-03 engine breathing paths. 4)	04 and Up engine breathing paths. 5)

Testing CC pressure on the dyno. 6)

Revised crankcase breathing is an area where you have huge potential to create unintended consequences.
Few if any really understand the ifs, ands and buts of all the factors the factory took into consideration when they designed the system.

Gappless rings while great for ring seal are another area where you can get in over your head if you are not careful. ⁷⁾
Wet sumping is only one potential problem you may encounter with them. ⁸⁾
In the right application they can not be beat but you better have your ducks in a row.