Clogging due to heat creep: buy new cooler or new hotend? Sadly, I am not able to "repair" my 3D printer. Every time, I want to print something that takes a bit longer to print, the extrusion stops at some point during the print (the first few layers are great), no under-extrusion whatsoever before that critical point.

I already tried temperature variation (185-220&nbsp;°C) with about 5 different brands of 1.75&nbsp;mm PLA.

I tried printing without any retraction, but failed (I also experimented with flow rate a lot and calculated the perfect percentage etc.)

Everytime a print fails, it is a nightmare to remove the PLA filament from my Bowden tube (because it expanded near the nozzle and is stuck in the Bowden tube). I have to pull with so much force, that I already cut myself several times because I slipped off my pliers.

As I know for sure (I already wasted almost 1kg of PLA for my testing) the problem is heat creep = heat travelling from the heat block to the PLA above because the heat break or fan seem to be broken.

So my question is: "Will it be enough to buy a new cooling fan (as the standard fan doesnt seem to be powerful enough)?" 

I have to add that I already bought the original hotend long time ago and I tried printing with the "fan of the first hotend" and with the "fan of the second hotend" (the fan that blows air towards the cold end) so that might not be the problem.

Or do I need a totally new hotend? (with heatbreak etc.)

My printer is a Creality CR 10, and I'm using Ultimaker Cura 3.6.

Or is it enough to buy a new heating block + heat break? (I don't know if the cooling fan is the problem or the heat break).
To fight heat creep, you must understand why this is happening. 

Heat creeps up the hotend assembly as a result of incorrect settings or hardware setup causing the filament to prematurely soften and swell.

It is important to reduce the heat travelling upwards in the first place rather than fighting the result. Too high print temperatures are an obvious culprit, but also print speed and retraction length are important. These need to be dialed in in perfect harmony.

Even when you buy a complete new hotend or parts for the hotend, incorrect settings may lead to the same results. It is known that all-metal hotends (due to the lacking of a thermal barrier PTFE liner in the heat break shielding the filament of excessive heat input) are more susceptible to encounter heat creep and should generally be avoided by less experienced makers. 

Whether or not you should buy new parts depends on the current extruder, your ability to fix it (and the willingness to put in more effort to try) and the knowledge to install new parts and find the correct settings for optimal printing. There is no unambiguous answer to this question.