I have experienced a premature rear bearing failure after storing the engine through the winter months, although only once. What I did was just prime the engine and start it. After about 6 flights I noticed that something was wrong, as you describe “some metal particles floating around”. Once I disassembled the engine I found the retainer ring of the bearing had failed, except for that the bearing looked fine no rust, races shiny,,,,My personal theory is that during the storage the oil viscosity increases, the engine is harder to turn. Being dormant for some months and suddenly spin at high rpm with this high viscosity oil may be too much for the retainer ring, or may be I just got a bad bearing? Your case sounds very similar to what I experienced. I agree with apereira that under normal circumstances that the rear bearing last 300 flights at least. Even though it is some work I would check it out so you do not damage your engine further, just my 2c worth.Arnstein