Yes, re-heat the original joints, add a touch of fresh solder if you think it will help, but not too much or you'll create a short. One expert I read in doing this uses a microscope to see the actual 'cracks'! I redid mine one year awhile back, and it worked great....for that one summer. Hasn't worked since, so I will go back in and re-do maybe this year just for the hell of it. I used one of those light/magnifying glass rigs, borrowed from the wife's jewellery shop and a fine point (I think 35W) iron, resin core solder only... and I was advised to avoid re-soldering the black IC modules in case the heat fries one, but this time I'll include them too. One thing is that it's hard to tell which joints you've done, so some get missed and some get done twice. Great 2 hour rainy day job though....and immensely satisfying when it actually works!

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1986 560SL
2002 Toyota Camry
1993 Lexus