From what somebody told me, Lie-Nielsen has excellent customer service. I believe the person actually damaged their plane and Lie-Nielsen repaired it for free so I would contact them. They'll probably have you send in the plane.
As far as stess relieving goes, I believe it's mostly done using ovens nowadays rather than just letting the casting sit, modtly due to time concerns and lean manufacturing.
Coincidentally, one thing Clico tooling who manufacture, or at least used to manufacture, the Clifton brand planes mentioned in regard to cast iron in planes, was that ductile iron wood bend rather than brake if dropped, however this could lead to inaccuracies in the plane. High strength grey iron like Clifton used, was less likely to bend if dropped, but if subjected to a strong enough blow, the castings would break, although Clico supposedly subjected plane castings to twenty foot drop tests onto concrete, and blows with a ball pien hammer to test the casting design, and their planes used a very fine grain high strength engineering grade iron.
Sorry for the above aside. Clifton planes used to get a bit of flak for the fact they used grey iron when they came out, so I figured I would mention the above.