It already has a copper washer but I think I've found the cause - somehow a solitary serrated flanged nut snuck in there last time I put it back together. These should be domed nuts, and I'm guessing a non-domed nut with an open top will provide a pathway for oil to seep down the threads? Also the serrations may not make an effective seal against the copper washer?
2 lessons to myself here: first, UV dye is great for finding oil leaks; second, I wouldn't have needed it if if I had been a little more careful when I put it back together last time.
I'm strangely relieved it's likely to be down to my error during reassembly, because the other option would have been to change the head gasket, but thats obviously a bit more of a pain in the a.
Looking at the exploded diagrams in the manual it seems all but 4 of the head nuts should be domed nuts.I plan replacing these all one at a time ( the rest are non serrated open nuts) retorquing as I go, trying not to disturb the head gasket. I will do that next weekend when my domed replacements have arrived. I'll let you know how I get on.
