NS40D2 leaking oil

Hello,
I have a NS40D2 ser# 47114 that is leaking oil from under the powerhead from where the upper pivot is. It runs under the splash guard and down the front of the driveshaft housing. After a 4 hour hour run it will leak about 15 mls or 0.5 oz of oil. Mostly it will not show up the same day but the day after.
The powerhead was rebuilt about 20 months ago. It has leaked oil from day one. Because of covid I just covered the boat up until 8 weeks ago. I have been trying to find the problem ever since. Things I have done so far are.
Removed the powerhead to check the seals and o-ring in the lower crankshaft head. All looked good but I replaced seals and o-ring with new ones.
Removed the intake manifold to check the gasket. No problem found. Replaced the gasket and reed valves.
Replaced all o-rings , gasket, floats. float needles in the carbs.
Removed the entire auto oil system. Tank, filter, mixing valve, all oil lines and removed the oil pump removed the oil pump drive shaft then reinstalled the oil pump to cover the hole. Ran the motor on 50 to 1 mix. Seemed to leak more.
I checked all the control rod lengths, checked timing, checked oil pump output. Checked mixing valve for proper pressure. Checked link and sync. All good per factory service manual.
All fuel and oil lines were replaced during rebuild and again within the last 8 weeks.
The motor runs great. Smooth idle good power. Compression 132 to 135 all cylinders. All spark plugs are a medium brown.
I am out of ideas. Please help. Thank You

Can you verify that it is 2-stroke oil, and not fuel/oil mix? It's not uncommon to get a lot of unburned fuel/oil mix in the exhaust of these.

Hello Paul.
Thank You for your reply. There does not seem to be any fuel in the oil that runs down the motor. The oil is about the same as in the container. The oil is not blue in color any longer. It is clean and the color of any oil that one would use in your car. When breaking this motor in with 25 to 1 mix for the first tank (12 gal) I did get some oil dripping out from around the prop. Went away when I went back to the auto oil system. That oil was black in color.
When running in a test tank I can not see any leaks or smell any gas fumes at all. Lower engine cover looks clean and dry.
Again Thank You. I need your ideas.

Very strange. Could be a drip from somewhere, but likely not after combustion, as, like you say, that stuff is typically black. If some oil was spilled while filling the tank, that could take quite a while to show up. I would super-clean everything and then later look for the wet spot.

Yes, Very strange indeed. What I have done yesterday is check a open container with some 2 cycle oil in it that's been setting for about a month. The oil is still blue. I wondered what would happen if it was mixed with gas then the gas evaporated out of it. Tested it and the oil left was still blue. I am thinking that any oil spilled or leaked with or without gas would still be blue when running out of the motor. At what point does the oil lose it's blue tint. We know the oil has a blue tint all the way trough the system and even in the carbs the mix has a light blue tint. Maybe when it atomizes with the incoming air trough the carbs. A air/fuel ratio of aprox. 14.7 to one I believe. Possible, but I do not know. When the air/fuel charge enters the crankcase with the heat involved. Again possible, but I do not know. I am going to remove the entire auto mix system again. This will let me see the left side of the carbs behind the oil tank. I will clean everything very well and run a 50 to 1 mix. If I do not find a leak and still have oil running down the housing. I will remove the powerhead again and reseal the case halves. That is all I can think of at this time. I will let you know what I find.
Again thanks for your help. Ricky

The color would stay with the 2-stk oil until combustion, then turn dark.

Update. I removed the entire auto oil system from the motor. When I removed the oil pump and it's drive shaft about 2 mls of oil ran out. This oil was not blue in color. It is the same color as the oil leaking down the motor. It is not black in color so, I believe it is before combustion. At this time I think my leak is coming from inside the crankcase. The seals and o-ring in the lower crankcase head, intake manifold gasket, oil pump o-ring, recirculation lines and balance lines have all been replaced during rebuild and again within the last 10 weeks. I now think It's either the case halves or a crack some where. Am I missing anything?
Thanks, Ricky

Try running on pre mix and see if it still happens.

When I was reinstalling the oil pump so I could run on a 50 to 1 mix I broke the pump. So, I had to order a new (to me) pump. I installed the pump without the oil pump drive shaft and ran the motor for about half an hour. It seemed to leak more. That sounds right because 50 to 1 at the rpm I was running it was about twice the oil as the auto system would supply. I removed the powerhead and resealed the cases. Could not see anything wrong but, I will find out. I am going to reinstall the powerhead sometime this coming week. I'll let you know.
Thanks. Ricky

Powerhead reinstalled. No leaks. Burning about 5 quarts of fuel per hour on a 20 foot pontoon running between 3400 and 3800. Does not seem too bad to me. Plugs look great. Time to go have some fun.
Thanks for all your help and ideas.
Ricky