string st = "";
            BinaryReader br = new BinaryReader(File.OpenRead(directoryItem));
            br.BaseStream.Position = 0xEED4; //4 Zeichen für Listennummer

            while (br.BaseStream.Position < br.BaseStream.Length)
            {
                foreach (char mychar in br.ReadChars(4))
                {
                    st += mychar.ToString();
                }
                st += "=";

                br.BaseStream.Position += 0x38c; // 
                foreach (char mychar in br.ReadChars(6))
                {
                    if (mychar == 0)
                    {
                        st += "999999";//bestimmte DS haben keine Nummer vorgegeben- setze universelle
                        break; 
                    }
                    st += mychar.ToString();

                }
                st += ";";

                br.BaseStream.Position += 0x2fa;
            }
            br.Dispose();

            string[] t = st.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries);
           
            char[] separatorArray = { '=' }; 
            HashSet<string> dedupl = new HashSet<string>();

            var res = t
                .Select(s => s.Split(separatorArray))
                .Where(x => dedupl.Add(x[0]))
                .ToDictionary(x => x[0], x => x[1]);

using System;
using System.IO;
using System.Text;

Encoding encoding       = Encoding.GetEncoding("iso-8859-1");   // what's the correct encoding?
const string searchText = "XSA40_DATENSATZ";

ReadOnlySpan<byte> data         = File.ReadAllBytes("Torni.dat");
ReadOnlySpan<byte> searchPhrase = encoding.GetBytes(searchText);

while (!data.IsEmpty)
{
    int index = data.IndexOf(searchPhrase);

    if (index < 0)
    {
        Console.WriteLine("Nothing found :-(");
        break;
    }

    Console.WriteLine($"First occurrance of searchText at position {index}");

    // Move behind the found searchText
    if (data.Length < searchPhrase.Length) break;

    data = data.Slice(index + searchPhrase.Length);

    if (data.Length < 3) break;

    // Move to first int-data
    data = data.Slice(3);

    string value = encoding.GetString(data.Slice(0, 4));
    Console.WriteLine($"Value found: {value}");

    // I'll break here, as it's just a demo for you ;-)
    break;
}