DSF

i tried all the settings from Medium to Heavy 2.

Medium does not print the image that well at all (big gaps)
Heavy 2 means it gets stuck in the fuser and you spend half an hour getting it out!

None of the settings inbetween these two provided satisfactory results either.

Looks like you covered most bases then with that testing!!! If the fuser is borked after it getting wrapped ring Oki and they will send you a new one FOC under warranty

Fuser is okay fortunately.

Target does list the 501 (or something like that) as a suitable printer for the paper, that model is only £159 approx so not really that much more than the 301 really.