I have a MK10 piston that has some corrosion at the base. I put it in the US with 1:30 SGC then 1:1 vinegar solution both for about 3 minutes. It came out pretty clean some corrosion remains. I'd like to hear from anyone if longer US times in 50/50 vinegar are harmful to a piston. How long is too long? I have a Crest US if that matters. Thanks.