Not because of parts replacement or adjustments, but because of the horrid amount of cleaning required to just get the machine useable.
A month or so ago I got a Singer 127 with a Chinese hand crank along with a 500 and a 185K from a forum member. The 185 took very little work to get it up and running. I actually had to do more repairs on the plastic case bottom than I did the machine. My wife stole it from me.
The 500 took about $35.00 or so worth of parts and a lot of cleaning, but it sews sooooooooo nice now.
The 127 .... I'm still cleaning it. I put the hand crank on Rusty and was contemplating on putting the 127 in a treadle.
But, I have never seen a sewing machine as grungy and filthy with built up, varnished, and solidified oil. Inside the machine is black. It honestly looks like an old car engine after 100,000 miles and only a few oil changes. That burnt on crud that looks like what you find in an oven that's not cleaned enough.
I'm almost betting it was oiled with the old cheap bulk car oil you used to buy in the glass bottles with the metal funnel built on the lid.
Kerosene wouldn't touch it. I had to buy a new jug of Hoppe's #9 to get started and that stunk the house up really bad. (Small house, too cold outside.) Once done with that I used denatured alcohol on cotton balls and q-tips to try to finish up with. But I'm still not done. Black icky cruddy oil residue is still leaching out of every nook and cranny. Yesterday I put it back together. I've cleaned everything and every place I can reach. But the Tri-Flow is dissolving some of the cruddy stuff so I've had to wipe it down a couple times now.
I've also been using cotton balls and oil on the outside and although I've gotten it cleaner, every time I run an oiled cotton ball over it, it's dirty.
I've had to replace one faceplate screw and the front slide plate. The slide plate that was on it wasn't correct and I had a correct one. Then I had to adjust the height of the feed dogs. That is all I've done to this machine other than cleaning.
Now I find that the top tension spring is so over strong I cannot get it to sew with the nob and spring on the tension. It simply will not allow the thread to pass through the discs. I borrowed the spring off my 66-1 and it sews perfect, so one more part to replace.
Then what? Is it worth using? Should I hunt up a treadle base for it? Put a motor on it and put it in a case? Boat anchor, door stop ............... I don't know. I'm just venting I guess. Sometimes I put way to much time in these things. If it wasn't for the decals, or what's left of them, I would have taken it to a machine shop and had them hot tank it like an engine block.
So, when is a machine just not worth the time and effort it takes to clean it? A rhetorical question really, as I don't know when to quit.