OK, found the oil leak on saturday at last, and its bad news - its the sump.
There is a slight crack on the top
bit of the sump, and the oil seaps through very slowly.. The oil level is just above the midway mark on the dipstick, this is 3,000 miles since I had an oil flush, filter and new oil. So by my calculations its used just less than 250ml (500ml between max and min mark on dipstick?) in 3,000 miles - a lot less than a twinny but it needs to have an eye kept on it.
Now the sump is shaped like a wellington boot, pointing towards the back end of the car. The crack is about 1.5 inches long, on the top of the 'foot', so very hard to see. We did try and seal it with some thermo-setting gasket sealant stuff, but not sure if it has worked yet.
How its cracked up there I don't know. Theres scrape marks on the bottom of the sump but no cracks or anything there..
If I can seal it I'll be happy, otherwise its new sump, or sump off and weld it. Definitely cannot be welded in-situ. Bugger.
I'll try and get some pictures up tonight