I've been printing PLA for about ten prints now, and in the last three I have noticed some darker splotches in the layers. I have noticed there is a bit of PLA that looks like it has been melted and pushed up around the black plastic towards the hot end cooling fins. This doesn't seem to bother anything, but I have noticed more and more black silicone "smell" and black/brown goo oozing down the hotend and blending in with the extruded PLA.

Does anyone have any ideas? I will pull apart the extruder this week to see if I can clean out the gunk, but would appreciate tips on how to prevent this from happening again. I have been printing between 200-225, with the best results being in the 200-205C range. Bed temps are 70C. My hotend cooling fan runs constantly when the printer is plugged in.