You can easily find the lines which go to the trunk lock actuator and fuel door usually as those are in the trunk, right near the actuators themselves...so start with those. If your leak is on the lock side then it is possible one of them is the source - you might just get lucky. If you don't have a mity-vac you can simply plug the lines to those two actuators and see if that fixes it...if so reconnect one at a time to eliminate it.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz