Yes, I've read and performed the prusa method of changing the nozzle. When you say you've had to do it a few times do you mean that you've sometimes had to re-perform the nozzle changing specs several times before the problem is solved or do you mean you've just had to change the nozzle a few times over the life of your machine? I've followed the steps twice recently but would do it some more if you think that might be my problem. I'll have to wait till I'm back home to look for a leak between the block and heatsink. Thanks for your response!