On my Black Jack, the kickout hits the pop bumper and bounces right back in, repeatedly. I tried slight adjustments, such as loosening the screws that hold the kickout mech in and then screwing them back in, or adjusting the angle of the playfield, but they had no effect at all. I thought about making new screwholes and remounting the mech, but the slot in the playfield doesn't have enough room to rotate the mech sufficiently for my new screw holes to not break into the old ones. Is there any way to change the aim of the kicker that I'm missing?

Looks straight and 'sharp'/square

Fins still there.

Pop bumper is freshly rebuilt, DC, and tuned to a hair. If it wasn't so strong I probably wouldn't have this problem. It seems like that kickout is just aimed right at the pop though...

For bending the arm, which way should I bend it to get the ball to go in a more clockwise direction? (higher)

I'm not sure if I ended up doing quite what you were describing, but it seems to have done the job...

It's not varied at all like you were describing but the heat shrink has made the kicker weaker, which sends the ball lower, which does make it not bounce back in...

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Mine was so bad I could leave and take dinner out of the oven and it'd still be going when I got back

One shot for an extra ball doesn't make very good competition... And if I shake it enough to disrupt it I tilt

Was describing the days I spent trying to adjust the kickout exactly right to a non-pinball friend when, after a moment's look at the hole he said "why don't you just put a, uh, one way thing in front of it?" 20 minutes of searching through parts bins later, I have 'solved' the issue completely:

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