When running the grounding electrode conductor to a transformer a really clean way to terminate is to run through the grounding lug that's mounted to the can unspliced on it's way to XO. From the lug to the XO it doubles as the main bonding jumper. I realize that in a lot of cases you could end up with a undersized MBJ especially larger transformers but it works well on the smaller ones. My question is does this violate the listing of the lug it passes completely through? (The one mounted to the case) I have noticed that the conductor tends to loosen easily when applying this method. (for this reason I don't really like it) Using a quad lug on the case and running a separate MBJ is probably a better way. Any thoughts?

I have 'run-thru' GEC's using siemens LK-2's on strips, no problem whatsoever.

The problem I've had with this has stemmed from the head of the screw that fastens the lug to the enclosure protruding into the path of the conductor. I tried flat head screws, but had to chamfer the hole in the lug to accommodate the screw's bevel (then thought I was probably voiding said lug's listing...no help)

Any more, I just use a 2 conductor lug, and be done with it.

Just substitute a listed lay in lug. These are open on one side to permit the insertion of the conductor without needing to feed it through. They have a forked opening in the end opposite the mounting hole.
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Tom

That's a great solve!

Dont forget to take a wire brush and scrape that paint off under and around the lug first !!