They have been around a long time. There are complaints of gear noise. Check out advance adapters. They have a lot of information about these units on their website.
Not to be a wise acre, but any chance it is the rear main on the 5.9 instead? New oil might be hard to discern from tranny oil. A more likely leak in my mind.
This is normally done to decrease the voltage drop to the bulbs, which increases headlight output. Just think of it this way, you are using the old circuits as the triggers for the relays. Main power from the relays come from the battery and goes out to the bulbs.