I didn't lose root when updating to JB, so I can't speak to how well this works, but here's how to Root an OG Razr/Maxx that's running JB.
[ROOT][Windows] Razr Blade: Droid Razr 4.1 JB root exploit - DroidRzr.com
[ROOT][Windows] Razr Blade: Droid Razr 4.1 JB root exploit - DroidRzr.com