The single greatest cause of nozzle blockages, and especially repeated nozzle blockages, is from incorrectly installed bowden tubes. It is not enough to just shove these things in and hope for the best, there is a method you need to follow and this is it.

I disassemble the hotend in this vid and show you how to correctly assemble and fit the bowden tube.

I forgot to say how to rectify the issue of the nozzle tightening onto the heat block, but basically all you need do is with the nozzle loose, rotate the heat sync 1 turn to screw the heat brake in 1 turn and tighten the nozzle again, if still no gap back nozzle out and turn heat sink another turn until the nozzle locks onto the heatbreak not the block.

Hopefully this will help you understand the hotend a bit better and stop you wasting money and resources on whole new hotends instead of just cleaning it and putting it back together.