UM3 Drooping/Melted layers

[Travis7s 1]

My UM3 is a year old and my prints have suddenly started coming out quite bad. I print with Ultimaker nylon and use a Printdry system, I am pretty certain this is not moisture issues, plus I have tried it with a brand new spool that was just opened. I print with stock profiles and I have done hundreds of these exact parts without issue. I seem to be getting extreme drooping/melting on layers that are not even on overhangs. I suspected some kind of cooling issue but did not notice any debris or anything inhibiting the fan. Cranking the fan speed to 100% drastically helps but does not get everything back to normal. Any ideas on things to look for that may be causing this?

I have attached some comparison photos for reference. The far left part is the "control" that i printed a while ago. The middle part is with cooling at 100%. The right part is with stock 40% cooling.

[Travis7s 1]

More troubleshooting: realized that it prints fine when I switched to the other nozzle so suspecting the printcore may be getting too hot somehow. I measured the resistance of thermistor and heater but it seems normal compared to the other core, at least at room temperature.

Edited March 14, 2019 by Travis7s

[Travis7s 1]

Brand new printcore seems to work fine so I guess this particular core has lost its ability to regulate the temperature correctly. The stats showed it as being hot for 20 days and printed 550m of filament. What is the typical lifespan of an AA printcore?