Piston engines that old go u/s all the time.
A more likely explanation for the grounding is that an issue has been found with the engine on one of the Spits (or maybe the Hurricane/Lanc) that's considered potentially serious enough to merit an immediate check of the rest of the fleet.
If the check involves complete stripping of the engine and/or precautionary replacement of a part that has to be specially manufactured then it's almost inevitable that the fleet will be grounded for a while.