I too have been following this thread with curiosity. The fact that the eng oil cooler is plumbed into the suction side of the eng oil pump disturbs me. Automotive eng oil coolers are rarely used in the gasoline world however they are extensively used in the heavy duty or diesel engs. I have been a Tech for the largest Caterpillar dealer in the world for the last 28 years. Every single Caterpillar eng ever produced has the oil cooler on the pressure side of the eng oil pump and is also downstream of the eng oil filter. To me it is logical to cool the oil after the pump and filter for the following reasons:
1) Pressurizing oil with a pump produces heat.
2) Filtering cooled oil has the potential to open the filter bypass valve more often and for longer periods of time allowing unfiltered oil to enter into the lubrication system.
3) Having the cooler in the suction circuit leaves the system open to extra possible leak points on the suction circuit. This would allow the potential for a constant stream of air to be entering into the lubrication system. Yes air will enter the suction circuit long before a visible external oil leak will be observed.

With regards to having air in an eng's lubrication circuit as per the original post. I have seen many times the devastating results inside an eng to it's components from air bubble implosions. An implosion is the result of an air bubble collapsing at high pressure allowing the surrounding liquid to impact the metal with incredible force. This can be readily seen on eng bearings, crankshafts, the coolant side of cyl walls, eng oil pumps and the list goes on. I have never seen this damage to a valve train component including lifters however for the most part Caterpillar engs use solid lifters. IMO the air that has managed to enter the system gets purged from the oil prior to entering the valve train components as this is near the end of the lubrication circuit. The comment in a previous post made about ensuring the hyd lifters be completely filled with oil is also very critical to valve train stability. Hyd lifters should always be manually pumped full before installation to the eng.
Unless someone wishes to convince me otherwise I will definitely be changing the way my Rotax eng oil cooler is plumbed. Because Rotax says so does not count here. My sincerest gratitude to the board members that have brought this fact to everyone's attention.