We are getting this lately: I use Brother printer, no matter how many times I do "cleaning" the print quality is still no good.
it seems this situation is quite common, particularly for model that uses LC37 or LC57. It's not gaps or blank, just bad and fuzzy. That we can confirm because we also use "Brother printer that uses LC37" (our model is MFC-260C).
The following might be the solution: It occasionally happens when your printing quality is set as "fast print", so try to set it (in printer's preference in printer driver) as "normal" or above and NOT "fast normal", see if the quality improves or not.
We found this solves in our case. Might solve for you too.
See "I use Brother printer, no matter how many times I do "cleaning""