Wing Mirror FIX 3x8 - step by step with links

I tried this fix and it didn't quite work for me, actually (on '86 328). The washer adds additional thickness (less than 1/8" or so) so that the bolt doesn't go in as far and ends up being flush against the plastic that it sits in. This, in turn, doesn't allow for the black plastic triangular cap to slide into where the indentation should be. I had to switch back to the original washer in order for the cap to snap into place.

Original on the left, new washer on the right (https://www.belmetric.com/external-serrated-cup-washers-c-563_579_1218_1729/wsescup6ss-serrated-countersunk-washer-stainless-p-11825.html?zenid=m9tb9ub1sbm9f8l7seipe9kev2)
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This is how it looks after I put the original washer back in, with the bolt going in further giving a lip for the cap to snap into. With the new washer, it was totally flush and cap won't stay on.
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On mine, I use the same screw and washer, put a dab of blue Locktite on the thread, tightened it up and whalah, it has been five years now and still tight.