This is why you Zinc chromate or anodise your threaded parts, not Powder coat them. JJR should know this.
All of my range of suspension arms are Zinced for this reason
Some good inside detials here, put them in your notebooks people.
As for thier coilovers, It is said that the Xa range is just D2, but Im not convinced. I think they are MDU by the looks of them, but obviously without pulling them apart its hard to say.
Either way, you can really expect this to be a great damper as they only cost $1500 per set (same as ISC :S)
You can expect them to last too long.
At least they use steel lower sleeves, thank god