Hard to tell from here Larry, be sure the bottom of the aircleaner isn't cracked.
The usual problem with finding these leaks is the mess they create. We have started using the florescent dye additive and a black light to pinpoint the origin.
After pinpointing the exact source you must take into consideration the amount of blow-by in the engine. That goes two fold here as the general pressure causes leaks plus it vastly changes the operation of the oil separator that is being drained here. The volume of oil can be significant at highway speeds with excessive blow-by.
A comparison would be the shingles on your roof. They seal perfectly in the rain but probably wouldn't hold out long under water.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician