Oil Pump or Rear Main Seal Leak
If fluid is seen leaking between the engine and transmission, check if the fluid is red or brown. If the fluid is red, it is automatic transmission fluid and the transmission's oil pump seal is most likely at fault. Always check the transmission fluid's color because ATF will turn brown from heat and oxidation. Rear main seal leaks are common, so if the color of the fluid is brown, it’s most likely oil leaking from the rear main seal. The rear main seal prevents oil from leaking past the spinning crankshaft flange. This is a common problem as an engine wears. If either of these seals are leaking, the engine and the transmission must be separated, and a new seal installed to repair this leak.