Per, CNR, Achim,
Thanks for calling in.
I use the local garden machinery centre for spare parts, from time to time. Unfortunately, they have different ideas about the value of used or salvaged parts, a tray of coffees will get you nowhere. However, I have found and ordered a model aircraft fuel tank with the correct rubber inserts which are compatible with petrol (gas).
Achim, I guess I will also use the Mannol AG11 coolant straight out of the bottle.
Cheers
Mike