Have Provents on both the '87 and the '05 Jeep Liberty CRD.
Try
www.airnowsupply.com , they're a little bit cheaper than Reliable Industries, both for the unit and replacement filters.
These filters are designed to handle 200 liters/minute of air flow, and last for a year before changeout on a 500 HP diesel. And if you're really creative, you can plumb the oil drain off the bottom back to the sump.
The one on the 2.8 L VM Motori engine in the Jeep is filthy black and soaked with oil inside of 3000 miles, drain a couple ounces of oil out the bottom each month.
The one on the '87, after 3000 miles it has a film of oil on the upper lip of the filter cartridge, and enough has dripped down that it's just starting to turn the bottom inch of the filter element from white to black, nothing yet in the bottom of the housing or the drain.
When I first got the '87, with 132K miles on it, there was so much oil collected in the inlet boot to the turbo and running down the side of the engine, it looked like the turbo drain was leaking big time.
I hate cleaning intake manifolds and intercoolers, so it was worth it in my book.