OooooooKay, here is a picture worth 8,000000000000000000000000000000000000000000000000 words
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In the pic above all the "O"s are oil points. The "G"s are grease points. I use Tri-Flow from Sew-Classic cos it's better.
The big square topped thing on the center of the cam stack is the retaining screw. You stick a screwdriver in the slot and turn it counterclockwise to loosen it. Then the cam stack should come up.
Literally everything there moves and needs oil. The two small vertical shafts on the left side of the cam stack is the selector shafts. Those gum up badly and then will not move. On this machine I used Hoppe's #9 Gun cleaning solvent. On my Singer 500 that's identical internally I used q-tips and denatured alcohol. Either or both will work.
After it's clean oil it with Tri-Flow and then spend some time running the controls through all their travels.
Joe