Inquiry About Coolant and Oil Leak Near Intake Manifold?

Hello,

I discovered a leak a couple of months ago coming from beneath the intake manifold, around a circular cup or plug approximately 0.75 inches in diameter. The leak appears to contain both coolant and engine oil.

I attempted to inspect the intake manifold by removing it from the engine, but I was unable to remove one of the bolts because it is located in a very narrow and difficult-to-access area. It seems that removing this bolt might only be possible if the engine is taken out of the car, which is not practical in my current situation. As a result, I have not been able to determine the exact source of the leak.

It may be possible to temporarily stop the leak using an appropriate adhesive or sealant. However, I have an important question: is there any possibility within the intake manifold for engine oil to mix with the coolant? If not, what could cause engine oil to appear in a leak from this location? Whenever the engine is started, coolant along with the engine oil is pumped out from the bottom of the manifold, near the circular plug.

I have also noticed black smoke coming from the exhaust. Initially, I assumed this might be due to carburetor misalignment or an issue with the distributor timing, so I did not investigate it further at the time. However, I have not yet checked these components, so I cannot confirm the exact cause.

For additional context, the car had been mostly idle for a couple of years. However, I would start it once a week and drive it briefly (about few kilometers) to keep it operational.

One more detail that may be relevant: about ten years ago, there was a coolant leak (without engine oil) from the same location. At that time, the leak was successfully stopped using a sealant that was available then, and the vehicle functioned normally afterward.

I would appreciate any guidance you can provide regarding the possible cause of this issue and how it might be addressed.

Thanks and regards,
SKM