The seal surface area on the 3.0L crankshaft can become worn after a time and not seal well even with proper installation technique. As Larry said, proper installation can be difficult to achieve for that seal on these engines.

Since you're having a shop do the installation, I won't suggest any ways to work around the installation issue - except to say that there is a seal surface repair sleeve available. It's made by Micro-Sleeve and sold through NAPA stores. Installing it is also an art form and can be problematic if the installer isn't familiar with repair sleeves. Done right, it's the best way to resolve the issue.

Frank