Yeah, it was hit or miss on those built-in clocks on that generation - that's what happens when you bid out to the lowest cost.
Some owners never had an issue with their clocks, some are still on their original clocks with no dimming issues at all. Some saw dimming right away, or their clocks completely died.
Re-soldering definitely is the way to go to fix these, but unfortunately, it is like it only works for a while - not a permanent fix. Even with a conformal coating to protect the fix, once previous/new corrosion sets in and/or traces start to open up / pad lifts - then the clock will dim again.