OK thanks to all, I have now had time to take another look, what I have, measuring from the top of the filler neck down is; a flange with a 3.5 cm hole 4 cm down. the oil return pipe, the centre of which is 7 cm down. 16.5 cm down is a large flange the size and shape of the whole tank. It has four holes in it, three side by side to the rear and one forward of the centre hole of the rear three. Each measures approximately 3.5 cm. There is no 5 mm hole. With the engine cold it is 23 cm to the oil surface. I made a dipstick out of a BBQ skewer. With the engine hot and running, the baffle with the 4 holes is covered by oil, the surface of which now lies at 13 cm so the level rises 10 cm when hot. Five minutes after switching off, the level is still 13 cm, falling to 13.5 by 10 minutes. I think the cold measure with a bamboo skewer is the way to go but does this description sound in any way familiar to anyone? Many thanks again. PM