Most critical point for having an oil-leak is without doubt the rear flywheel. For type 1 engines, BBT has 3 different stock seals at unbelievable prices. The best seal for a Type 1 is the silicone-made one, with double lip. The seals are manufactured by BBT itself, meaning there’s a constant quality control. You can also count on regular deliveries. All engine seals are sold individually.