Oil leak down top of bell housing on driver's side

The car is a '91 OCC. Is the pressure sending unit for the gauge in this location on a '91 OCC? I'm having a hard time seeing behind the valve cover. It is a pretty slow leak, not even pooling.

It is above the oil filter.

Thank you Fred. Only other things I could think of to check are Valve Cover and Intake Manifold corner. Is there anything else that high up that would leak on the bell housing?

Gasket under the distributor.

Thanks!

Intake manifold end rail seal. They are RTV and always start to leak over time. They always run down the bellhousing and nearly every "Rear main seal leak" is actually this leak.

Weird, our 1990's 307 Olds V8 leaks coolant at the back of the intake when it sits for long periods. Strange that the SBC will leak oil instead.

I will also check the distributor because I had trouble getting the rotor off when changing it and had to use a screwdriver to pry it off. Maybe I loosened the seal.

The rotor is notorious for sticking to the shaft. Removing it in that manner should not make the gasket leak. I have removed a couple of them and never caused a leak.

Okay, probably the intake then.

smparr wrote:

Weird, our 1990's 307 Olds V8 leaks coolant at the back of the intake when it sits for long periods.  Strange that the SBC will leak oil instead.  

I will also check the distributor because I had trouble getting the rotor off when changing it and had to use a screwdriver to pry it off.  Maybe I loosened the seal.

The leak is at the end rail. Small piece that runs between the cylinder decks. Very old engines had a small rubber gasket there but it always blew out so it was ditched in favor of a nice bead of RTV. RTV doesn’t last forever so it will eventually leak. Not leaking coolant because it has nothing to do with the gasket that seals the coolant passages.

Very common issue that folks with SBC engines are accustomed to. Never owned one that didn’t need a reseal done. From a 1967 327 to a 1995 350.

I got lucky on my '96 Roadmaster and '93 Caprice Wagons in the early 2000s, since they had lower miles they didn't leak any oil. My '70 98's 455 leaks oil but from valve covers and the '90 OCC leaks miniscule amounts of coolant from the intake and oil from the valve cover. Valve covers are much easier to fix.

Intake gasket leaks are also very common on the SBC. I had one on my 1989 Trans Am spring a leak. Normally not a big deal but it was 1998 and I was living in Germany at the time. Needless to say I had to wait on those parts to arrive.

Most rail leaks are seeps, Class 1 for those with military experience. They don't cause any real issue until they progress even more so if it is low mileage and untouched because the engine plant does a good job most time. Me? I put my hand back there and check on a regular basis. I absolutely despise oil leaks of ANY kind and don't want them on my car. I hate when a customer brings me a disgusting oily mess to work on.

Cleaned the back of the engine and bell housing and put dye in the oil a couple days ago but no signs of a leak yet. Driving her daily. So this is either a super slow leak that built up a lot of nasty dirt over time or maybe it's residual spillage from oil changes. I guess only time will tell.