Seems like you're really enjoying hating these (nameless) a/c boxes.
You make no mention of their energy-efficiency- which should be a major
factor in decision-making IMHO. Not to mention that your in-wall a/c
installation is likely a major air-leak.

Are you bound to having wall mounts?

Steam-cleaning? Not likely necessary unless you have lots of crap in
the air, or don't use a filter. You might pop the cover, give the fins
a spritz with garden hose, and oil the motor bushings. Do check that
low-side water drain hole is not blocked.

Presuming that, like most here, you're into DIY.

HTH,
J