When I did the gearbox oil change last year, before it died, I researched the issue. Apparently early on, when gl5 oils were first released, the gl5 additives that coat and attach to the synchros are stronger than the brass. When they are worn off, they take a small proportion of the brass with them. I was assured by Nulon that the problem had been rectified with more modern oils. But now I'm not so sure, so I will have to shell out for the gl4.
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