Oozing plus bad adhesion?  

Oozing plus bad adhesion?

I've had my kit-assembled MK4 for just over a year. For most of that time, I could easily print using PLA, PETG, and ABS. I've been using the Prusa brass nozzle 0.4mm. Recently, my son started a print and left the print unattended. For some reason, the nozzle gouged the design into the plate and then printed on top of that. It was a job he had run before. I'm not sure what happened there. Since then, I have had all kinds of print problems.

1. When the nozzle is hot, filament tends to ooze out. This seems wrong, but when the print starts the cleaning usually (but not always) clears most of it. However, when the nozzle is traveling, the oozing can create loops of filament that interfere with new filament being extruded onto the plate or other layers.

2. When the print starts, the initial border extrusions often fail to adhere to the plate. As the nozzle moves to make new extrusions, the unadhered filament interferes and starts to collect and pull up any new extrusions. If I am attentive, sometimes I can catch this and snip the dragging unadhered extrusions. this allows that layer to proceed, but future layers will have nothing below and fail.

3. When first layer does succeed, it often curls up slightly in a kind of feathering that trips up future layers.

I am not exactly sure what is the problem I'm trying to solve: oozing, bad first layer, dragging, hairy prints? It seems like all of them or possibly several.

I have tried:

• cleaning plate (prusa satin powder coated sheet) with IPA for every print. sometimes helps, but not every time
• cleaning nozzle with brass brush - don't see debris or damage on nozzle
• cold pull
• re-calibration and tests (multiple times)
• entering a global Z offset of 0.3mm (this helped a little, but not consistently from one print to the next)
• using different and new filament - I first had problems with 8 month old PETG. Same with 8 month old PLA. Same with 1-month old PLA. I'm using Overture filaments and default temp settings. The printer is in my attic. Humidity is 49%. Temp is 27.2C.

Can anyone suggest diagnostics or fixes for these issues? This printer was so reliable from the first prints after assembly and now, unusable.

Help, please.

second print, first layer of second shape did not adhere consistently

first print, first layer of second shape did not fully adhere and began to lift up so I ended print.

second print, first layer of second shape did not fully adhere boundary extrusions. see gap behind nozzle

second print, first layer of third shape did not adhere and got dragged until I paused