[keith888]

Thanks Neil. I assumed that the bleed screw would have a copper washer of some sort that could do with a change. I'm pretty sure the tank and rad are OK as there were no incriminating dried blobs of antifreeze around them. Based on the deposits the bleed screw or leaking hoses/clips look most likely. Radiator sealants always seem to provoke controversy even though many manufacturers use them from new! I take your point about the small coolant passages though so I'll try without and see now I get on.

Keith