* Rear Main Seal: This is the most common culprit for rear oil leaks on a small-block Chevy. The rear main seal seals the crankshaft where it exits the engine block. Replacing this seal requires removing the transmission, which is a more involved job than gasket replacement.
* Valve Cover Gasket (Rear): While you mentioned replacing all gaskets, it's possible the rear valve cover gasket wasn't properly seated or is a faulty replacement. Oil can sometimes migrate down the back of the engine and appear to be coming from the rear main seal when it's actually the valve cover. Recheck this area carefully.
* Timing Cover Seal: A leak from the timing cover seal would be visible near the front of the engine but could run down the back side.
* Oil Cooler Lines/Fittings (if equipped): If your engine has an external oil cooler, check the lines and fittings for leaks.
* Cracked Block or Engine Case: In worst-case scenarios, a crack in the engine block itself could be the source. This is less likely if the leak is relatively small, but it's a possibility.
Troubleshooting Steps:
1. Thorough Cleaning: Clean the engine thoroughly with a degreaser and high-pressure water (carefully, avoiding electrical components). Let it dry completely. This will allow you to pinpoint the exact source of the leak when it reappears. Use a non-chlorinated degreaser.
2. Run the Engine and Observe: After cleaning, run the engine for a short period and observe where the oil is leaking. Use a flashlight and carefully examine the entire rear of the engine.
3. Dye Test (Optional): Adding a leak detection dye to the oil can help pinpoint the source of the leak, especially if it's a small seep.
4. Professional Inspection: If you're not comfortable performing this level of engine repair yourself, take it to a mechanic specializing in classic or muscle cars. They have experience with these engines and can properly diagnose the problem.
The most likely culprit is the rear main seal. Replacing this is a significant undertaking and requires mechanical skill and the right tools. Unless you have experience with this type of repair, it's best to seek professional assistance.
