Here's the list:

1. The Nell motor issue is only on original factory motors. Once replaced with a new one, it works fine (mine does anyway).

2. Usually the "Lion" plastic inside the backbox animation is worn from being on a higher powered lever that makes it pop up faster. You can find all 3 plastics, but usually the Lion is the only needing to be replaced. There's a fix going around about how you can re-wire it to the same lower powered lines supplying the other two levers, but I've personally not had to do this. You'll want to cut some self-adhesive padding to fit the bottom tray where the hat trick plastics rest so they don't receive such a shock when dropped back down by the levers. Prevents wear & tear.

3. Backglass: Just about every used backglass for this machine has a worn spot on Bullwinkle's nose. Here again, I found just cutting a square piece of self-adhesive padding and putting it on the screw head is enough to prevent this kind of damage.

4. B.O.M.B. targets and the Hat Trick Targets will all need re-gapping if buying used and unshopped. These targets are no longer made, but I found some colored targets that look identical from Pinball Center in Germany. They are slightly wider by 1 millimeter, which means they don't fit through the holes, so I had to feed them in from the top of the playfield and then install the hardware to them from underneath. A little tricky, but well worth the effort if needing to replace them. For the Hat Trick targets, some thin self-adhesive padding in the heads will prevent "wrong-wrong-wrong-hat" when they are struck by the pinball (along with proper switch gapping of course).

5. Often times the ball diverting arm on the upper plastic ramp is improperly adjusted. This causes it to swing open too wide and nick the ramp plastic over and over until there's significant grooves ground in. Simply adjust the positioning of the arm with the tightening the screw such that the arm cannot open to the point of hitting the ramp at the corner.

6. Hitting the right orbit shot can cause the ball to drain straight down the middle on its return down the left orbit. This can be caused by anything from a poorly aligned metal barrier, dirty playfield, or improper inclination of the machine. It's a very picky issue that was even addressed in a bulletin update back when the machine was still new.

7. Sometimes you'll find a used machine without the original "Start" and "Boris" buttons, but these are easily obtained from online dealers. The thing to watch out for though is the launch button metal housing assembly. Those are no longer available from online dealers (last one I know of was purchased last year).

8. The ramps on heavily used machines are typically thrashed at the entrance. There used to be replacement ramps made for the left "WABAC" ramp, but these are out of print as well. If you can salvage the originals, put cliffy protectors on them immediately. Not only will the protectors prevent further damage, but they also do a decent job of hiding existing damage. I was fortunate enough to find a complete set of NOS ramps in Norway, and so all of my ramps are in perfect condition (woohoo!)

9. Plastics: There are some rather poor reproductions floating around of the slingshot plastics, but you can often find NOS versions on ebay. For the other plastics, you can find some of them on Bay Area Amusements, but beyond that, you have to get lucky with ebay. I recently hit the jackpot when somebody put up an auction for a complete set of NOS plastics, which are now installed in my machine.

10. Return lane guides: Often you'll find these are in bad shape in old machines. The original "dip" design is no longer made, but you can get new "smooth-curve" ones made by Stern that work perfectly fine if you have to replace them. Some modification is required for the bottom set by sawing/sanding off the posts on one side. Here again I got lucky and got a set of originals in good condition from another pinsider in Bulgaria.

11. Decals: Public machines will often have sun-bleached issues on the pie display and pop-bumper caps (the red ink on both turns completely yellow over the years of UV exposure). The caps are unobtainium, but the pie display decal can still be purchased from BAA (I believe they have one left).

Beyond that, there are just the universal issues that come up like worn out solder points on the various boards. I recently replaced the PSB with an X-Pin model and was very happy with it.