Ultimaker Original+: print has lumps and small gaps are being filled
What is wrong here? Is the printer over extruding? Is the temperature too high? Is the flow rate wrong? Am I missing something else?


It is always difficult to diagnose problems from a set of pictures only, and without the original model to compare it with, but yes, from the pictures it looks like your printer has a severe case of over extrusion, possibly in conjunction with a thermal problem.

The first picture in the set is particularly interesting for a number of reasons:


The chequered pattern of the top layer looks like being generated by the nozzle "digging" in the layers below and rising the plastic around it.  A well calibrater printer should have a top surface with a very subtle texture instead.





The teeth of the comb and the gap between them are inconsistent, as are the shape of the tip of the teeth.  This let me think your printer actually doesn't operate consistently, over-extruding in some places a lot more than in others.  A pinter should be able to accurately replicate its performance along the full length of the comb instead.





The plastic has a different finish and colour in different places.  Namely, it looks burnt and glossy where the worse print quality is, white and matte where the problems are not so bad.  Both the colour and the finish let me thing the plastic in the dark spots have been heated way over its operational range and/or for too long.


In essence what I think it is happening (mind it: this is just a theory) is that your printer is over-extruding and in addition your hot end may have issues with keeping its own temperature constant and within the designed limit.  Other factors that may also play a role could be:


Wrong settings in the slicer as for example a nozzle diameter set to 0.5 mm when it really is 0.4 mm instead, or the filament diameter being wrong.
Blobs of over-extruded material forming and sticking to the nozzle, where they take too much heat for too long and burn before "falling" in the print and damaging it.
Filament that is old/of bad quality and that has impurities in it, or has an inconsistent diameter along its length (thus causing over-extrusion in places, but not in other).
A nozzle that is not well fixed to the heating block, thus allowing molten plastic to seep out from the joint and run down on the outside of the nozzle and ultimately on the print itself.
A nozzle that got damaged and whose opening is not circular and/or not matching its nominal diameter.
The extruder hobbed gear not e"biting" in the filament and thus the filament slipping at times, thus being inconsistent in the quality of material being extruded.


So, here's the the trouble-shooting I would go through at this stage:


Check your printer setting in the slicer.  Doh! :)
Take a close look at how the print works while in operation.  Do you see blobs forming and sticking to the nozzle?  Plastic seeping out from places it shouldn't?  Is the nozzle round and true?  In case of doubts, just change the nozzle with a new one (it is a less-than-1€ part anyways), easily outspent by the cost of filament in a failed print.
Calibrate you extrusion (and thus your flow-rate) by performing accurate measurements over at least 3 length of filament.  Matterhackers has a nice how-to that you can follow for this.
Manually check the diameter of your filament (at least 5 measurements at at lest 200 mm distance between them) and adjust the corresponding "filament diameter" setting.
Calibrate your temperature by using a test tower.  This one has extensive instructions on how to use it in the thing description, plus is customizable directly from thingiverse.
Print again your model and see how/if your changes affected the print quality in any way.


If the above fails, you could also try to use another slicer, but it's unlikely the problem is with the software.

UPDATE

I'm not familiar with your printer model, but the updated pictures seems to show the leakage happening between the heat block and the heat break, rather than between nozzle and "whatever". ;)

This can actually be caused by two different problems (or the two of them compounding).


The two parts, which are normally just screwed together have come loose.
If your extruder is not "all metal" (which is normally not the case in most printer), the PTFE tube (the whitish plastic tube the filament slides into) may have dislodged upwards, so instead of being a tight fit in the heat block, it leaves room for the molten filament to seep upwards.


In both cases, a reassembly and thorough clean-up of the head is in order.  I would suggest trying to find specific documentation for your printer online, but the general process is:


warm up the head to printing temperature.  All subsequent steps will have to be done at this temperature (wearing protective gloves is highly  recommended)
remove the filament
remove the PTFE tube
remove the nozzle
remove the the heating block from the heat break
wipe as much the plastic as possible (bit drills work well for the hole in the heat block
increase the temp a further 20-30 degrees
reassemble everything
profit


Please note:


the heat break is relatively fragile: be gentle when unscrewing.  When removing/attaching the nozzle is worth keeping the heat block in place with a spanner to prevent twisting the heat break
if you can't remove the plastic when molted, you can try letting it cool and scrape it
it essential that the re-assembly be done while hot.  Metal expands with heat, so what feels firm while cold will eventually become loose at high temperature