I managed to clean it eventually - compressed air helped a lot - in case it's useful to someone else, with the saw lowered remove the saw blade and clean as much as you can using tissues and a long reach brush - I used one of those made to reach inside bottles. Then fully raise the saw and clean from below. Lubricate and move up and down a couple of times to spread the lubricant. It's not quite butter but much better than it was!
