I bought this fuel tank for a Guzzi special project, now abandoned. At the time it was not clear to me, or the seller, which model it came from - it had the lovely shape and lever-closure filler cap I was looking for. 

I have now done a bit of research and I am fairly confident it comes from a Stornello 125. The final photo is for illustration purposes only and shows a Stornello with a tank just like this. Please note: on my tank the closure lever pivots to the rear of the filler hole. This seems not to have been true for some Stornellos, which pivoted at the front.

The shabby black paint hides a tank that is good, clean and solid. I cannot find any significant dents or anything more than surface rust. The seams and both fuel tap bosses are clean and solid. Only surface rust can be seen inside - as picture 9 tries to show. Seal looks good but will probably ned renewing after all this time.

Sadly, I never got round to needing to put petrol in this tank but I cannot see any reason why it would not be fuel-tight and usable.

The photos capture the quality and integrity of the tank well, so please study them. I am happy to answer questions and provide more photos.