Bearings wear out, thats a fact as death itself.
1Qwksport2.5r, One possibility I have seen in some industrial machines is when changing over to lube oils with a different baseoil or even very different additive packages is that there is sometimes some oxidation effcts within the oils themselves, hence I always recommended a flush out of the machine with the new oil, drain and refill before recommissioning the machine,
with a model engine in the environment you operated yours, the water and its properties of hardness or salinity could be have been a contributing factor over and above the simple change out.
The occasions when I changed fuel I always flushed the engine with the new fuel and lube before running it. Just flood it and run it off the start for about 10seconds. I always found the engines to want to run a little rough on the change over but with the flushing they simply fired right up and ran well.
Not too mention that the Synthetic component would also have increases the detergency of your lube oils and it could have losened rust from elsewhere in the fuel path and that deposited on the rings.
Very hard to provide a definative answer sorry but your story is interesting and worthy of further consideration