That is the flaw with the first two versions of the K1 series hotends; the nozzle heatbreak interface tends to expand slowly during use.
Creality’s fix is the unicorn nozzle setup; there is an upgrade kit.
K1 Series Ceramic Heating Block Kit—Quick-swap Nozzle Kit for K1/k1 max/k1 C
Most, like me, have switched to the MicroSwiss Flowtech setup. I have never had any issues with filament leaking, and I have changed over both my K1s.
Currently, the Flowtech doesn’t work on the latest version of the Creality heatsink without modifying the heatsink; if you have this one, then the Flowtech is not a direct drop-in.
Creality Unicorn and MicroSwiss Flowtech nozzles can be cold-swapped (no heat-up required). The Flowtech’s benefit over the Unicorn is that MicroSwiss has more types (wear resistance plated brass, CM2 harden, Diamondback, and CHT high flow) and nozzle sizes (ranging from 0.1 to 1.0 mm) and is adding more as time goes on.