Presser foot lowers slowly on Singer 99-13
 

When I put the lever down the foot doesn't lower along with it, it kinda glides down. Like if you've ever seen a piano with an anti slam keyboard lid. It's just come back from the shop and I guess they didn't think it was an issue or they would've fixed it but I see in videos that other people's machines don't do that. I decided it was probably decades old dirt and unscrewed the screw on top and took out the rod there (arrow 1), and cleaned the grime off it and the attached spring with alcohol, and put it back in with oil at arrow 2 like there should be (I'm actually in a different state right now and of course forgot to take a picture of my machine before leaving, and don't know what the parts are actually called, but had the oiling diagram saved on my computer), and also cleaned where i could reach of the part at arrow 3. If there was a change it was minimal. I stuck a couple q tips inside where the rod came out of and there was black stuff that came off but I didn't use alcohol on those ones. Why not? I don't know. I was tired yesterday. So I think I'll clean inside of there when I get back home, but is there something I'm overlooking? And anything better to use than alcohol?
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Prolly not it but you mght want to gove a bit of oil to the left lever and the slot it rides in. And also a drip where it bumps the tension assembly. You are certainly on the right track. Welcome to the board.

Put sewing machine oil on area above #2 and below #3 area. Put paper below needle area to catch the run off oil, keep working the lever up and down. You will probably have to clean the lever lift also. That is the silver bar that lifts the foot. Get some pipe cleaner, the white fuzzy wrapped wire and use for cleaning in the tight spots, old t-shirt material is great for cleaning. I think you should let the people who worked on your machine know that they did not clean it enough.

One point commonly missed is where the presser bar (hollow rod) moves up and down in the black cast iron part of the body. It's obviously and oil point, but still frequently overlooked. The part that moves up and down with the presser bar lever need oil both inside and out side (I hope the description make sense). All moving parts behind the flaceplate needs oiling; all parts linking the presser bar lever to the tension release pin, jonts, hinges etc. Theres equivalent points on the needle bar. I don't use alcohol on the black cast iron parts, it will cause damage to the shellac, use oil, spray can oil for dissolving dirt and grime, but in general you get very far with the basic oil. My 99 became very smooth when I turned to teflon oil (like Triflow and Finish Line Ceramic Wet lube). The spring in the presser bar needs to be oiled too.

Isopropyl alcohol and a Q-tip works fine on old oil. Just make sure it's the 99% stuff.

Your presser foot shaft is probably gummed up with old oil. Work some alcohol though the surfaces then replace with oil.

Please don't use 3-in-1 for that. It dries up into a varnish.

I'm not an expert on alcohols, but etanol and metanol will damage shellac, and likely gum up the presserfoot shaft worse. Alcohol will dissolve the shellac, make it gummy and liquid, before it dries again. I'm not sure what isopropyl alchohol does, but for parts in connection to the black paint be careful. Spray can oils like WD-40, Weldtite Teflon spray doesn't (but can harm gold decals). Basic sewing machin oil does the job too, it can take a bit longer but tentantive applications of basic sewing machine oil and moving parts will eventually flush out dirt and grime.

I fixed it! Removed the presser bar and soaked it in kerosene and now it’s working again

If you remove the entire bar it's just as easy to polish it up with something like Quick-Glo. Presser- and neelde bar usually shines up like new. Make sure you regularly apply new oil to the areas involved, it's a must :- )