This is usually caused by a failed print like you suggested, often because the print did not stick onto the buildplate adequately. I would aim to re-level your buildplate a bit closer. (after you clean your head). This is usually NOT caused by leaking, but actually by the head getting clogged and the material running upwards into the heater block.
This should not be ignored or allowed to 'seal' itself. The heat from the nozzle block will run off into the material and into the fan shroud and continuously drip into your print as well.
To clean the material off your heater block, heat up your nozzle to 90C via maintenance -> advance -> heatup nozzle. When it hits 90 wait a few minutes and then take off the fan shroud. You need to unscrew the 2 screws on either side of the shroud above each fan that goes into the head housing.
Once you do that take off the fan shroud by pulling it downwards. It maybe a bit sticky since the material may be stuck onto it. Sometimes it's easier to remove the nozzle first. (this can be done at 90C with the proper hex nut.
At 90C, the material should be soft enough that you should be able to peel off the gunk that's around your heater block as a whole piece. If it requires too much force, heat up the nozzle another 10 degrees.
Once removed you should be able to put everything back together and it'll be as good as new, cleaner even, its like a waxing for your nozzle. .
Once you get the bed nicely leveled this problem rarely happens.
Having read many threads on this issue I would like to add that in my case ignoring the problem and letting the leak seal itself is not working, I get large blobs appearing intermittently on prints. Heating the tip does not make removing the material easy since there is so much of it it remains solid, and further,, it is wrapped around the wiring entering the area above the hot tip. I have a Ultimaker 2+ that is less than 2 weeks old. I am thinking the leaking problem is more than I want to cope with. I am no longer satisfied with this product.
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