I have a Rotax 912 ULS that's about 7 years old with about 470 hours on it.  I am recently experiencing low oil pressure at higher rpms although it's OK at idle to mid range rpms.  I put a mechanical gauge on the engine so I know that the low pressure is not just an indication issue.  Oil level is also correct with a fresh oil change of Aeroshell Sport Plus 4 and Rotax oil filter, part number 825-016.  

On a ground test with the mechanical oil pressure gauge hooked up, the pressure starts up at around 60 to 70 psi (depending on outside temps of course) and warms up after about 5 to 10 minutes to around 40 to 50 psi at idle.  Oil pressure remains above 30 psi until I go to full throttle and then it slowly but steadily drops below 30 and keeps going down until I ease up on the throttle as I don't want it to get too low.  Otherwise, the engine sounds great and temps are well within normal range.

Will adding the Rotax shim to the oil pressure relief valve help resolve this problem?  The engine has the newer style bolt with ball and spring but no shim installed.  Or is this a more serious issue?  I recently received an oil analysis report from Blackstone Labs that reported my oil's lead content was high even though this engine has always used unleaded premium auto gas.  Could I have a worn bearings issue maybe that's causing the low oil pressure at high rpm?  Other ideas, thoughts?

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