We had the same problem with our Bell 407's.
Overfilling the main txmn will lead to oil being vented out the pressure release valve on the txmn housing.
We leave our levels just below the yellow line (normal min mark) and above the bottom screws. This level seems to prevent the venting of txmn oil. If overfilled, it will vent till it finds its own "comfortable" level, it’s just messy! High or low skids don’t make a difference in the txmn levels. Then very important to check for correct levels 20 minutes after shut down when the oil is still warm.
BUT NOTE: The transfer we experienced was from the main txmn to the engine. I am not sure if it will transfer from the engine to the main txmn. Apparently it won’t happen, but I stand corrected.
If you have a transfer problem where the oil transfers past the damaged/old labyrinth seals on the drive shaft at the free wheel unit, there is no indication in the cockpit on the engine or txmn temperature gauges when transfer occurs from the txmn to the engine during a normal flight, if it hasn't been an extended flight, in my experience. That is as I said transfer from the txmn to the engine.
The only indications will be on the after flight. There will be excessive oil in the oil tank, visually visible through the engine oil level sight glass. If you open the engine oil cap, oil will come bubbling out the now very full oil tank, causing another fine mess. You will also notice a drop or slight drop in the main txmn oil level sight glass, depending on flight duration and severity of the leak rate.
Apparently there is no limit to the rate of transfer according to our engineers, as long as the txmn levels stay in limits. The seal must however be changed as soon as possible as 555 in the engine oil system is not ideal, as it hasn't got the same properties for cooling and lubrication as with 560. It also has to do with the fact that 555 don’t have the same high temperature performance as the 560, even though they are both synthetic oils.
You are worried about an internal leak. The chance of an internal leak is very remote, if not impossible.
Hope it helped. Overfill seems more likely to be your problem. Good luck.
