Can anybody advise please? Very slow loss of coolant from system and will try Radweld (has worked with other vehicles in the past), but how do you mix to radiator system as there is no filler cap. You7 do not usually add to expansion tank...

do not do it --rad is vey small core on c2 and will block easily .
find the leak-maybe the header tank cap is not hlding pressure.
if nowetness can be found on bottom of rad core or hoses

Many thanks for the tip. Is radweld really that aggresive? Does it actually block the radiator cores? I thought that once it reached a certain temperature it only solidified when it oxidised, i.e. came out through a leak?