I'll have to admit, I've never had one apart other than take the lower element out. .I just soak 'em in a bucket of diesel for a day or so, then start sloshing it up and down in the bucket 'til no more dust/oil/dirt comes out. Then I do it once more for good measure, let it "drip dry", put it back on, refill the cup and it's good to go.
John,
when you do get it disassembled, douse the steel gauze element in diesel and set it on fire. It will burn up all the oil and any dirt contained there in can just be shaken out/tapped on the concrete, then follow that up with a quick rinse with mineral spirits or gas or some such.
Cheers,
Neil.