A good friend of mine had the exact same result as you did. He asked by the machine shop if he used mobil1 oil for initial breakin, which he did. He was told this was a big mistake and very prone to have problems like you had. I had never heard of any thing like that, but they swear by it. So use a good quality motor oil, but no synthetics. I'm sure this has something to do with the ZDDP like George was talking about.
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