Lol, none of my Alfas with leather interior ever had a lovely smell of leather, esp compared to some of the old English sports cars I remember. THAT was a great smell, wouldn't mind it in my 91S, but alas, that smell isn't there. Is there a leather treatment which will duplicate it, or was it because of the way the English tanned or finished the leather? The Italian leather in the Alfas always seemed like nothing.
And, yes, isn't it just amazing that when driving around, you can definitely smell what ever the driver ahead of you is smoking, esp since fewer people are smoking nowadays, thank god. Because you are now less likely to smell the smoke, it is more noticeable it seems. Unfortunately, vaping now seems to be the ugly habit some have. Ack. How can people do that to themselves, lungs being so important.
Anyway, sorry, back to car smells, oil on the exhaust pipes can certainly do it, esp if driving around with a partially open window or sunroof, and with bad hood and trunk seals. It's how I check for gas seepage in a car, esp the vapor recovery mess in the trunk of the 164.
Also, I did have to change the filler neck hose in the 89 Milano, as the one provided originally in the car did leak fumes into the car, it not being vapor impervious. Installed a vapor resistant one from Goodyear. Much better,