In the past I've serviced a 51 vac and aero, but I agree with you. I tend to prefer to go by the If it ain't broke don't fix it rule whenever possible. So if you don't want to take the risk of having iron from an IG ink precipitating out and clogging the collector in a Parker 51 and you simply *must* use IG ink, then use it in a different pen.
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