I ordered an Ultimaker last November and got it running this January. I had pretty good luck with it for the first month or so (only printed about 10 small prints in that time), until I got my first plug. I got it fixed, but I'm worried that the problem is going to persist. No matter how hard I try to put the extruder head together, I get some PLA leak out the top of the heat block (attached picture - sorry bad quality). My question is mostly preventative as it is working right now - is this a sign that another plug is on it's way? Screwing it in tighter doesn't seem to work. I'm printing at 220C right now. How in general do you avoid this problem? I've made sure that everything is put together as tightly and securely as possible. Thanks for any insights.