351 C intake leak?

I have oil leaking at the back of the intake on the block where the sending unit is. The unit is NOT leaking, I'm wondering if I have an intake leak. I try adjusting my Holley and with the screws turned all the way in, it doesn't seem to change the sound of the engine. I've had some problems with the enging filing out the plugs before I've ever pulled it out of the garage.

Thanks,
The motor in newly rebuilt, it does look like the gasket in the rear is pushed out. It was professionally rebuilt so I wouldn't have these kind of problems.....oh well.
The holley was purchased 3 years ago, drove a couple of miles, then the car was parked and torn apart for rebuild. I just had the carb rebuilt and it seems fine. I am having a problem with timing. The car will not start unless I advance the timing. Then if I drive it, I get the pinging and gas smell, I retard the timing and it does fine, until the next day, then it won't start unless I advance the timing....again.
The car is not really streetable yet, I still have lots of work, interior, tail lights, markers, etc.

Thanks