I just had this done to my 2007 GL450, under warranty thank heaven!
It was a shock to visit the dealer and see my *new* GL sitting there with a gaping hole in the engine compartment!
Thankfully, they really took their time and the tech working on it was a senior tech with experience. They had already done a few of these. They replaced a few other items there as well, everything covered, including all the solenoid units. I took a look at the engine afterwards with a critical eye and things looked really good, nothing out of place.
I asked the tech if there were any stray bolts left at the end, he just gave me a look...
Talk about a massive job for a tiny part. He showed me the worn gear, the teeth were visibly worn, substantially so. The engine appeared to be in excellent shape otherwise, everything clean and no signs of wear.
Oh, and they also fixed my wouldn't-stay-shut coin tray.
C.