On today's engines and transmissions the oil leaks are not as common as 20 years ago. Seals and gaskets and the design of components have come along way. With today's climate in the winter and summer months and driving with the windows up fumes from leaking oil can easily get into the cabin and cause grief for passengers and the driver. Fixing leaks to avoid the fumes is a must. leaking oil from certain gaskets and seals can eventually get onto the wires and soften the insulation which will lead to other issues in the future.