My STLE came with the additional screw that apparently some of the newer machines didn't have. I removered the screw and replaced with a longer screw and added a standard Black Mini Post Ring that you get in all Pinball rubber replacement kits. The ring sits at the level where the ball is the widest. The ball has not yet gotten stuck in the area in question. As a matter of fact, you ball won't even sit there even if placed in that spot.
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The washer idea is a good temporary solution, but metal on metal will eventually (3 years+) create fine metal bits that will damage the playing field over time.