I'm still waiting for the history from the garage, but I'm told the trans oil had not been changed for some considerable time. I've pulled apart the filter I removed originally and found a few black bits & a few metal particles in the filter medium when flattened out - not enough to cover a small fingernail in total.
I'm almost resigned to having the box rebuilt, though it doesn't seem to be getting any worse. Is this a job I could undertake myself? I've never attempted an auto box before, though I have rebuilt manuals & plenty of engines.
As a desperate measure I'm thinking of trying a Dexron III fluid (instead of the cheap Dexron II I've always used) & a gearbox conditioner additive. Is this worth a try?