m000493 method seems to perform some kind of XOR encryption. This means that the same method can be used for both encoding and decoding the text. All you have to do is reverse
string p0 = Encoding.UTF8.GetString(Convert.FromBase64String("OBFZDT...")); string result = m000493(p0, "_p0lizei."); // result == "gaia^unplugged^Ta..."
return m0001cd(builder3.ToString()); changed to