What I've done w/ my machine. Well, #1 is what I want to do--a little help on that, please! :]
1 - How do you fix the inconsistent rattly plunges?
2 - Loki Lock sensors. Ball gets stuck. Get sticker from Stern. Ball gets stuck less. Get creative & tweak for hours until it never sticks.
3 - Slings launch balls. Put small rubber self-adhesive foot on coil stop for slings. Balls launch only occasionally.
4 - Hulk sticks balls under elbows. Disassemble Hulk, put rubber self-adhesive foot on mechanism, raising Hulk's lowest arm resting position a bit. That helps.
5 - Hulk sticks balls under elbows still. Disassemble switch plate, scooch down playfield electromagnet that's slowly destroying switch plate. Fuss with assembly until the slightest pressure makes the switch close. That helps moer.
6 - Hulk sticks balls under elbows still, but not often. Considering taking a file to his elbows to increase the gab between the PF wood & his elbows. These parts of the arm don't show anyway.
7 - Ball sticks on Tesseract cube turntable. This doesn't seem to be adjustable (like the PF window in Congo or the bookcase in Addams Family). I had only 1 or 2 sticks here.
8 - Ball sticks on Hulk drop targets. Only once or twice. Ball search will kick it out if you wait.
9 - Ball sticks on both transitions of bridge. Tweak bridge to minimize gaps at both ends.
10 - BW ramp shot often doesn't make it. Raise the roof at the top of the BW ramp entry portion (not too high or bridge hits glass & gets stuck in up position), slightly raise the BW spinner, lower the bridge resting position, bend back the back wall of the post-bridge fixed U-channel if it's impeding ball flow.
11 - Ball drop into Hulk saucer often bounces out. Get fix from Stern: an extra plastic.
12 - (Optional) Replace random red/blue/green Christmas tree lights color scheme with a tasteful selection of bulb colors.
13 - Put a bit of blue painter's tape on the fluorescent tube in the backbox if you want to see Hulk instead of a bright white glare (for AVLE Blue, at least--can't comment on other flavors).
14 - Set Avengers difficulty down a notch from factory settings for everybody except Hulk.
15 - (Optional) Hulk's right fist knuckles are probably scuffed from scraping the bridge. File or sand or paint or whatnot as desired.
16 - If you move the right outlane post to "easy" position, the ball will often wiggle up into the gap you've created above that post. Add another post or stretch a rubber across this gap.
17 - Buy some some power transistors on your next pinball order. If you hold the flipper for a minute or two to cradle the ball, you'll blow a transistor. Learn to remove & install 3-leg transistor packages.
18 - L-shaped -36 plastic behind Hulk. Mine was broken. Stern sent me a replacement. It had 2 extra spiky pieces pointing downward, nested within the triangular rubber by Hulk's left elbow. I'm not sure what purpose they serve, but they seem to be a late-model upgrade from what I had in my machine.