Ever since the engine was rebuilt in 2003, the oil consumption has been a concern. I have been losing 1 quart of oil every 2.5 - 3 hours.
Normally, this would indicate worn rings or sealing issues. However, the plugs are not oily, and a recent visual inspection of the cylinder bores showed no evidence of excessive oil fouling or ring/cylinder damage. This is an engine that was completely rebuilt with new pistons, rings etc. as part of an overhaul to make the engine "yellow tag" throughout, with all ADs complied with. The cylinders are chromed, which usually results in slightly higher oil consumption, but slower wear rates. The cylinders are the cylinders which were on the engine prior to overhaul; minor repairs were made to the exhaust valve area on 2 of the cylinders, and they were re-plated.
The engine has always had high oil pressure since the rebuild. If the oil is not completely warmed up, takeoffs result in an indicated oil pressure of 105 lbs/square inch. (I can't be sure that this is a true reading since the pressure guage has not been calibrated recently).
I have always suspected that the high rate of oil loss was not due to oil being burned in the cylinders, but that it was mostly due to oil being expelled from the breather. The breather currently exits in the right wing root. On long flights I always find oil on the lower cowling, and after 2+ hours the oil has run all of the way down under the rear of the boat tail. If I run the engine at high rpm for any period of time, I also find oil streaks on the prop after landing. This is clearly oil that has been expelled from the breather, not oil burnt in the cylinders.
18 months ago John Hooker fitted a Slime Fighter air/oil separator. This cost me over $150 from Spruce. However, the separator was not fitted in the correct vertical orientation due to hose constraints that existed at the time. In its current configuration it makes no measurable difference to oil loss.
I am going to adopt a Plan A. I will make 2 changes in the short term and evaluate results:

1. Re-position the existing air/oil separator to be vertical
2. Install stainless steel tubing clamped to the exhaust to re-route the breather outlet and vaporize material being expelled via the breather downstream from the separator

If (1) does not reduce the rate of oil loss, I will adopt Plan B. This will involve buying a more expensive air/oil separator (probably the M20). This air/oil separator has a separate return line for oil that condenses in the separator housing. The main installation priority will be to position the separator close to the engine (probably anchored to the engine baffle) so that its internal temperature stays above 212 F. This will hopefully result in water products blowing through the separator and out of the breather tube, instead of condensing and running back into the engine.
More on this change as I proceed.