Date registered: Jun 2019
Vehicle: 2007 SL550
Location: Dallas, TX
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I just went through a similar situation with a new-to-me 2007 SL550. In the end I:
1. used the liquid wrench, jacking up one side at a time so it would pool at the bolt and not just run down the wheel. One day each side.
2. bought a $100 Bauer electric impact gun at Harbor freight.
3. Added 3 ft of pipe extension to my 1/2 inch drive 24" handle breaker bar.
After the liquid wrench soak, the electric impact wrench got all but 5 of the 20 loose. The pipe extension on the breaker bar did the rest.
Mine are lug bolts, not lug nuts. Heat would only make them expand and be tighter in the threaded hole in the hub. Freeze spray might have helped, but I ended up not needing it. Inspecting the bolts, it seems rust was at least as big an issue as over-torquing.