After five years owning my second-hand 9900 I think I found a secret in keeping the heads clog-free. Get a professional cleaning and maintenance service call from an expert and the head cleaning issues go down drastically.
I had my 9900 cleaned and the pumps/capping station repaired earlier this year no longer have to run numerous cleanings. This week, after five weeks of sitting while I was on the road, I ran a test sheet upon my return. It needed a simple cleaning and I was back in business.
Before the service, I'd need to run the cleaning cycle, sometimes a couple of times a day. Now perhaps once every week or so and I'm not running this thing daily.
I wish I had figured this out years ago...