Hi. My car is actually an Autobianchi Bianchina Panoramica - so basically a 500 Giardiniera ina different frock!
Yesterday, she wouldn't start so got the AA out. After hours of trying, we got her running but have found that she's over fuelling and the oil is now full of petrol. She'll be going to a local mechanic later.
Has anyone else experienced this problem - and what was the cause?

Most likely the diaphragm in the fuel pump breaking down and leaking petrol into the sump. Also a possibility of cracked float in carb or worn inlet valve not shutting off.

Toshi 975 said:

Most likely the diaphragm in the fuel pump breaking down and leaking petrol into the sump. Also a possibility of cracked float in carb or worn inlet valve not shutting off.

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Yes, fuel pump diaphragm is the most likely culprit, had the same with my Giardiniera, without a shutoff valve the fuel is syphoned in the crankcase even as the car stands still. Two cures:
1) Install an electric shutoff valve coupled to the ignition coil.
2) Repair the pump with kit from Axel Gerstl that has a double membrane and a tell-tale drip hole in the spacer between them.

That's excellent! Thank you. Is there a website for the Axel Gerstl kit or could you give me a pointer to where I could buy it?
Thank you.

Thanks for the tips. She'll hopefully be getting looked at tomorrow. I'll keep everyone posted.