OK, here we are, right back at page 1 or 2 of the discussion again. The Mr. Slim model you crave isn't much bigger or better than the model you found for $50. Both are R-22 units, both are single speed compressor, both will lose capacity as outdoor temperatures fall. Both units fall on their face below -9 degC outdoors. The mitsi looks to have been decommissioned and stored better, maybe somebody shined it up before they tore it down.
If seller installs the mitsi, and you try to modify anything, there goes your package warranty deal. Are the red diamonds and word of mouth worth the money you might not have today anyway? We don't know, but it sure is getting cold outside...
Quick and dirty page you seek:
https://www.manualslib.com/manual/69...page=15#manual
The msh-30rv service manual is easy to find. The units didn't change much at all until the -wv came out. It runs off R410a, so the plumbing changed but not the specs. Then they came out with the hyper heat models and everything changed.