Talk to the mechanic: The leaking fluid that I originally brought my car in for is indeed engine oil, possibly from the rear main seal. It seems they stopped investigating the source of this after discovering the alleged crack.
Asked the mechanic if he was positive it was a crack, and not just fluid coming from the sensor and pooling along the drain line. The mechanic is positive that the fluid is coming from that line, that it is differential fluid, and that it is not leaking from the sensor. The store also claims they did not remove or tighten the sensor. Looking at my service records, I also haven’t replaced the sensor in the time I’ve owned it.
This shop does not handle differential repairs and recommended another shop. When I started the car, the check engine light, vision off, and vehicle dynamic control warning light all came on, none of which were on when I got out of the car or had ever been on before. The shop tows the car back to running the codes and resets them. The codes were Engine (P0171/P0174 for system on bias ribs 1 and 2), A/C (B14A1 sun load sensor circuit open or low), and vision (B2806 ECM abnormal). The dash lights no longer come on after restarting the car. It’s unclear what caused this, and the shop says the only things they removed from the car were the plastic skid plates and the engine cover.
Current Status: Assuming there is indeed a crack along the spill line, I’m looking for a shop that will replace the differential and rear main seal while they’re at it. Thanks for any additional advice.
