如何更改现有加密/解密代码上的填充选项

我有以下代码，它工作了近两年。但是现在我们开始看到填充的随机问题。当我说随机时，我的意思是同样的事情在某一天起作用，但在另一天不起作用。有一天，它决定随机工作。

现在，如果我像上面的答案中提到的那样将填充添加到none，我可能会弄乱所有先前加密的文件。我正在考虑在catch块中使用GOTO语句创建不同的方法，就像我在更改加密密钥时所做的那样。或者是否有更好的方法将填充更改为None?

/// <summary>
/// 
/// </summary>
[Serializable]
public static class EncryptDecrypt
{
    private static string EncryptionKey_old = "MAKV2SPBNI99212";
    private static string EncryptionKey = "Yi9BpGG1cXR01gBwGPZRTOznoJHpkGBOzisBg5jl3iRu48yhcFGdZu76fDpa5FUu";
    /// <summary>
    /// 
    /// </summary>
    /// <param name="clearText"></param>
    /// <returns></returns>
    public static string Encrypt(string clearText)
    {
        byte[] whitebs = Encoding.Unicode.GetBytes(clearText);
        using (Aes encryptor = Aes.Create())
        {
            Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(EncryptionKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
            encryptor.Key = pdb.GetBytes(32);
            encryptor.IV = pdb.GetBytes(16);
            encryptor.Mode = CipherMode.ECB;
            encryptor.Padding = PaddingMode.PKCS7;
            using (MemoryStream ms = new MemoryStream())
            {
                using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateEncryptor(), CryptoStreamMode.Write))
                {
                    cs.Write(whitebs, 0, whitebs.Length);
                    cs.FlushFinalBlock();
                    cs.Close();
                }
                clearText = Convert.ToBase64String(ms.ToArray());
            }
        }
        return clearText.EndsWith("==") ? clearText.Remove(clearText.Length - 2) : clearText;
    }
    /// <summary>
    /// 
    /// </summary>
    /// <param name="cipherText"></param>
    /// <returns></returns>
    public static string Decrypt(string cipherText)
    {
        int attempts = 0;
        string exception = string.Empty;

        StartHere:
        cipherText = cipherText.Replace(" ", "+");
        byte[] cipherBytes;
        try { cipherBytes = Convert.FromBase64String(cipherText); }
        catch { cipherBytes = Convert.FromBase64String(cipherText + "=="); }
        using (Aes encryptor = Aes.Create())
        {
            Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(EncryptionKey, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });
            encryptor.Key = pdb.GetBytes(32);
            encryptor.IV = pdb.GetBytes(16);
            encryptor.Mode = CipherMode.ECB;
            encryptor.Padding = PaddingMode.PKCS7;
            try
            {
                using (MemoryStream ms = new MemoryStream())
                {
                    using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateDecryptor(), CryptoStreamMode.Write))
                    {
                        cs.Write(cipherBytes, 0, cipherBytes.Length);
                        cs.FlushFinalBlock();
                        cs.Close();
                    }
                    cipherText = Encoding.Unicode.GetString(ms.ToArray());
                }
            }
            catch
            {
                if (attempts == 2) throw;
                EncryptionKey = EncryptionKey_old;
                attempts++;
                goto StartHere;
            }
        }
        return cipherText;
    }
    '

现在更改这个不是一个好主意，我也不知道我该怎么做，因为我们用这个代码加密了成千上万的文件