Rear main leak.

Hi, my name is Devin. I am an auto repair expert with the Car Genius team here at RepairPal. I'm sorry to hear you're having trouble with your vehicle. With persistent rear main seal leaks on your Mustang, especially since the engine was rebuilt, there are a few potential causes. First, check the crankshaft surface where the seal sits; any scoring or wear can prevent the seal from working properly. A worn or improperly installed seal retainer can also lead to leaks. Verify that your crankshaft has no end play issues, as excessive play can cause the seal to move, breaking its effectiveness. Additionally, ensure the PCV (Positive Crankcase Ventilation) system is working correctly; a clogged or faulty PCV valve can create crankcase pressure that forces oil past the seal. If you need more advice, have any other questions about your vehicle, or would like to get connected to a RepairPal Certified shop near you, we have you covered. Give us a call at 877-913-1554, and we will happily help you out!