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.
1986 300E 5-Speed 240k mi.