I've had to literally chisel off the oil pan on a Ford 2.9L V6 that was factory installed with the grey Ford RTV. We tried everything. Carb cleaner, brake cleaner, I even tried the smallest wound guitar string I had. I had to go back and GRIND the remaining pieces of oil pan rail off the block with an angle grinder. I've never seen anything like it. That pan would have never leaked had we just taken all the bolts out. It was ridiculous.