A piece of Mylar? You can also use washers UNDER the ramp to elevate it slightly. Also make sure to butt the ramp up against the wood tightly.

On the kickback, I would check the stop and the coil sleeve for alignment and dirt.

Fill in the gap (let's see a picture), and check if there is a divot where the ball drops beneath the VUK.

Make sure you have it set in the settings to be on at the beginning of the game.

I might be set to off and won't come on until the "light bounceback" targets are hit.

On the kickback not retracting issue check that the opening in the apron is not scraping the side of the kickback and not allowing it to retract. Apron can be easily adjusted. Guessing something is grabbing the kickback and the flipper use shakes up things just enough to free it.

The other thing you might check with the kickback is the position of the switch arm. I had one that wouldn't fire every time and it turned out that I just needed to adjust the switch. But, like vid1900 says, if the red instert is not lit, it souldn't be kicking back. There are various settings for it in the menu.

That gap between the ramp and the upper playfield behind bigfoot is probably the trickiest thing with White Water. If you don't have a Cliffy Protector there I would get one now because if you don't already have a divit in the wood from the vuk kickout you will get one evenually. Anyway, even with the Cliffy the ball can still get caught. What I have done on mine is to take off all the ramps in that area until you can access that area and see what's going on clearly (yes, it's a pain but it's worth it). Adjust the Cliffy Protector placement so that the protector is flush with the ramp. Then get out a pinball and try to get it stuck in that area. Start making adjustments to see if you can get it so that it will not stick there. You may have to experiment with washers under the ramp or the Cliffy, or with different tightness on the screws holding down the ramp, etc. You may even have to get into looking at the way the left ramp side meets up with the left metal ball guide. What you are likely to find is that you'll be able to get it so that a moving ball ALMOST never sticks, but that if you roll it slowly enough you'll be able to make it stop there. Just try to get it as good as you can.

The other thing that can affect this area is how the back of your playfield is leveled. If it's leveled correctly, the gravity will usually prevent the ball from hanging up there. The only thing is, you pretty much have to take off the entire upper playfield and the ball guides in the back to get a level directly on the playfield back there.

I've been able to dramatically reduce stalls there but frankly, I've never been able to entirley eliminate it. I might get a hangup once in every 75 games or so.

Not using your finger, but an actual ball; does it trigger the kickback with the glass off when cold (just turned on)?

+1. That's how I figured mine out.