I think the spray is a waste of time and way more messy than necessary. Clean out the lint. Go into the bobbin area after you have removed the bobbin race and thoroughly clean out all the lint and built up dried oil, drop a little oil on the moving parts or places that will rub. Clean lint off the bottom of the machine - drop a little drop of oil on the moving parts. Go up into the nose - clean out any lint or dried up oil. Cleaning dried up oil is not absolutely necessary - it just looks better - BUT you do have to worry about dried up oil in the moving parts. Tri-flow will penetrate and loosen it up. The zz slant machines have a pin the needle bar rides on - that will need lots of attention - the other pin it works off of is below the camstack and to the left - if you push on the needle you can see it. Those get caked up and the machine doesn't zig and zag. If you don't get it completely clean the patterns will not look right - the needle won't swing all the way left and all the way right or it will do slow motion. The cam stacks readers will need to be cleaned - PITB IMHO - takes time. Clean up all that moves and then re-oil. You will need to grease the gears. The first time I did it was a disaster - I sprayed WD40 all over the place then I used 3-in-1 oil on the whole thing - gumbo gumbo gumbo.
Sew-classic has lots of slant-o-matic accessories and good bobbins.