This has all been very helpful - and I'm sure will have been useful to others too.
I'm not sure I ever expected to say this, but I am going to take Adrian's advice and try wire brush and Fertan, as I'm not too keen to work with unfamiliar power tools while wedged upside down in a gas locker. I've ordered some (and some Owaltrol Oil as well today). It won't get done til Easter, but I'll try and remember to report back. I find maintenance logs as interesting as trip reports. -- Nigel Stanley
