As an experienced electronics tech, I can tell you that cracked solder connections on anything will make you want to pull your hair out. Typically this problem can occur from one of two big causes...or both. One is heat, which usually comes from a high current (not necessarily high voltage) situation. The other is stress, due to insufficient wire slack or something that causes a constant "tug" on the connection. In either case, if there is an insufficient amount of solder on a connection, then over the years a crack will develop. In the beginning stages, your symptom (whatever it may be) usually starts out intermittent (happens once in a while), but gets worse and more frequent over a period of time. Insufficient solder quantity is becoming more and more of a problem these days on many electronic products, because there is less and less "human" involvement in doing this job in the factory. So while the quality of the work may look fine as the product goes through its quality inspection process, the quantity of solder is very likely at the bare minimum. Now, as I see it (and this is only my opinion), in the case of the intermittent odometer, it seems that the cracked solder connection is probably caused by stress on the connector pins due to very little wire slack from the cable that plugs into it. I don't think that it would have been high current, because LED displays do not typically draw much current at all, so it wouldn't get very hot. In either case, though, it probably would not be a bad idea to solder ALL the connections on that plug. At least you would be improving the solder quantity at that point, and you probably will never have that problem again.
My 2 cents
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