Rub the beef with the salt, pepper, mayonnaise, mustard, ketchup, thyme, garlic and olive oil, coating it thoroughly. Cover and refrigerate for at least 2 hours, preferably overnight.
In a large skillet over high heat, sear the beef until deeply browned on all sides. Transfer to a bowl and wrap tightly, first in parchment paper, then in aluminum foil. Roast in a 480°F (250°C) oven for 30 minutes. Reduce the heat to 340°F (170°C) and continue roasting for 2 hours, until the meat is fork-tender.
Meanwhile, prepare the pickles: In a jar, combine the onion, chili, allspice, bay leaf, soy sauce, vinegar and salt. Pour in the boiling water, seal and let sit for 30 minutes, then strain and set aside.
In a small bowl, toss the sauerkraut with the mayonnaise. Spread mustard on each slice of bread. Layer with the cabbage mixture, warm slices of beef, pickled cucumber, onions and chili. Drizzle with the mustard and olive oil mixture. Close the sandwich and serve immediately.