Manhattan, IL
Gottlieb Volcano (1981)
There's a playfield subway covered with a stainless steel flap.
The previous owner for whatever reason used small nails to hold the back of the flap down on the playfield. I removed these nails and was left with a very rippled metal edge that would catch the ball. I tried bending it down and taking out the ripples but it just made things worse. Eventually, I cut off a quarter-inch strip of the flap removing most of the damaged metal, and patched the playfield smooth. Things improved but it wasn't right and the ball would still catch here.
The dotted line shows the damaged area that I had to cut away. The flap is also somewhat beat and tired looking... depending on temperature, it would open a bit and not stay flat. A couple of little dings and ball wear... yes... it's actually 0.0005" (half of one thousandth) thinner in the middle where the ball travels.
Unfortunately, this flap is made from 100% pure Gottlieb unobtainium. I mean absolutely nobody sells these - not PBR, not Marco, not even eBay. There isn't a part number in the service manual or the 1982 parts book. EDIT: The manual and parts book call it out as a "Chute"... "45 - B-20995, Ball Return (Chute)"
So how difficult could this be to make?
It's sheet stainless steel that is exactly 0.006" thick (I obtained and used type 302). It was originally made with a custom die in a stamping machine, but that's way way too expensive for only making one/several pieces. You can't cut with a shear because of the curves and inside corners. You can't cut it with a snips because the edges would deform and prevent it from sitting perfectly flat and flush with the playfield. You can't cut it with a CNC laser because the heat would likely (or maybe not?) permanently deform the edges; moot point as I don't have one.
I decided that a Dremel cut-off wheel would be the best way.
Then carefully do the layout.... black Sharpie ink and a carbide scribing tool.
I used a straight edge to make the line that restores the area I previously cut away.
I carefully drilled out the holes backing them up with wood. Then I used the Dremel to cut within ⅛" of the outside of the line. I got right up to the line... and I mean exactly up to the scribe line with an air file. A 60-grit 3M Cubitron belt takes it down quick and throttling the belt speed with the trigger gave me enough control to not overshoot the lines. The air file was also used length-wise to ensure the sides stayed straight and true to the line.
The end-wheel on the air file is the perfect radius for cutting the inside corners too.
Here's my first new one (top) and the original (bottom)
It's a dirty and tedious job leaving you covered in metal dust, but only took maybe an hour of intense concentration and work... so I made another new one and now I have two reproductions in addition to the original.
I finished it by hand sanding all the edges smooth with 320-grit and then polishing the whole thing with 1500-grit in one direction. Then a coat of wax. Of course it had some curvature because the steel comes rolled in coils and it's very springy, but some gentle massaging can bend and work it flatter. As long as it's not kinked or bent too sharply, it will respond favorably to this persuasion.
Here's my second version installed in the machine. The flap now sits dead flat on the front and back edges where the ball rolls over. It's still curved downward slightly to ensure the flap says shut. Get it too flat and changes in temperature will make the flap open/close slightly.
IMG_2746 (resized).JPG
IMG_2747 (resized).JPG
The one back edge looks jagged in the photo but that's an optical moiré effect caused by the sanding lines and the light reflection... the actual part has edges that are straight and silky smooth.
I have no idea if any Volcano owners would need my spare new flap... but I have enough extra stainless here to make 8-10 more flaps if needed. 
EDIT:
Important! Leave one or both top posts loose or the flap will very slightly fluctuate with temperature and not sit flat across the top. Just loose enough so the plastic post can turn by hand. Just enough that this will prevent the metal from binding up. It's something you can barely see but when it's warmer, it wrinkles up just high enough that the ball can get hung up on it when rolling slowly. By leaving the top post loose, the metal is free to expand/contract without getting hung up and causing this tiny bump on the edge. I recommend the top post on the right (closest to the playfield), since this one post will free up the entire right side of the flap. As long as it's not bent, the flap should sit perfectly flat on the playfield around all sides. It should be able to sit flat without any of the screws or posts holding it. If not, consider replacing it.
I believe this is the root cause of the entire issue. The ball was getting hung up on the top edge so somebody tried fastening it down with tiny nails. Of course, this was a disaster, made the problems worse, and the whole reason why I had to make an entirely new flap.
