Under extrusion  

Under extrusion

I am new-ish to 3-D printing and bought an MK3S and it was working great. Then suddenly started what appears to be underextruding.  It is a bit strange to me because it will print the first few layers OK but then it underextrudes and prints the rest of the file as shown below.   I printed a solid 20mm cube and that worked fine. I printed a 3DBenchy (tugboat) and that printed fine.  I have tried clearing the hotend nozzle per Prusa instructions and that seemed to improve the problem but not fix it. I want to try a Cold Pull clear but I can't see how to "manually insert"  or "manually remove" the filament.  Is it necessary to remove the extruder stepper motor and filament gearing to do this?  I don't want to start disassembling things if that isn't necessary.

I have order a new hotend, but it won't deliver for a few days. It seems strange that this would happen after a few months.  The printer hasn't had excessive use.  It has been running regularly (and printing good parts) for the past week, but prior to that, it was used once or twice a week - again with no issues.