In order to ensure water cooling of the engine, there is a labyrinth of hoses that allow each part to be supplied with coolant and therefore also with heating. Between the cooling pipes there is a distribution room where the pipes meet at different points. This manifold is made of plastic, as are several parts that relate to water cooling. Mainly due to temperature changes, plastic hardens over time and as long as you don't touch it, it can last a very long time. Only during disassembly are you confronted with the brittleness of the material and parts may break and need to be replaced. Although the manifold part may still look good, you should check for cracks before replacing it. If in doubt, it is advisable to replace it.
The reason you have to work on the valve is probably to replace or loosen the cooling hoses. If you don't have a new cooling hose yet, look under the related parts tab, the available hoses listed there are directly connected to the manifold.
Caution : During production of the manifold, plastic offcuts may have remained behind, inspect the interior and remove the offcuts before assembly.
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