I have a 1985 Westfalia with a 1.9liter engine. My question is about the nuts that hold the steel coolant pipes attached to the water pump. I know they are not 12 mm but I don't know what they are so I don't know how to remove them. They are round and appear to require some type of an allen wrench. I cannot find the appropriate wrench in my collection. Is anyone familiar with this set up who might be able to tell me which type and size wrench I need?