When motor is cold, put a gloved hand over the tailpipe.
If there is a leak, you will likely hear the hissing of exhaust coming from a leak near the front.
If it is very difficult for your hand to resist the pressure, or the motor stalls, you probably do not have a leak.

Look for oil leak on the motor, probably on the hot (exhaust) side.

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1986 300E 5-Speed 240k mi.