To drain residual oil and sludge from your gearbox, you need to remove the sump on models built up to 1971. Later, this sump was fitted with a sump plug, making draining much more convenient.
On older models without a crankcase plug, you'll still need to replace the gasket, which isn't necessary on newer models.
But given the advanced age of the vehicle and its often unknown maintenance history, it's a good idea to dismantle the sump to clean and inspect it properly before pouring in new oil.
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