Was this before or after you swopped out the IPDM and the BCM ?
If after, I would check that the fan motors are working, in fact I would check out the fan motors irrespective.
Alex.
Stuart, there are tests and procedures to check out a starter motor, however it may be a plan just to remove the starter motor and bench test it.
Guaranteed fully working pre-owned starter motors are in stock if required.
Alex.
There are no O rings, only oil seals which are part of the cover, however you will have to replace the gaskets if you remove the cover as they form a seal between the cover and the head. You have a leaking oil seal in this instance. Alex.
You have an oil seal failure, however the seals are integrated with the cam cover. Solution is to replace the cam cover or live with it as it should not develop into an issue. Alex.
All 350Z cars have traction which you can partially switch off if you wish. Mines is permanently off. as I find it a more pleasurable driving experience. Alex.