When CylcArt repainted my current Capo (S/N 40324), I did ask them to apply a rust preventive coating to the insides of the frame tubes. I have not worried about rust on my other frames. Having said that, I also admdit that internal rust MIGHT have contributed to two of my frame failures (1971 Nishiki, seat lug of BB shell; 1973 Peugeot UO-8, right chainstay between clearance dimples). I was able to ride both bikes home safely after they broke, as I did when my crashed-and-restraightened 1960 Capo (S/N 45211) finally ruptured at the front end of the downtube.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069