the MAF on the 2001.5 onwards S4 is a hitachi unit and is more reliable than the older Bosch unit. Both units are not interchangeable...
We think the oil supply line design on the S4 was changed on the MY99 onwards cars. There is an Audi US technical bulletin advising US dealers to change the lines on earlier cars.
The 2001.5 cars have extensive changes - no F hose, changed Inlet Manifold, revised spec turbos, revised intercooler/lines, Hitachi MAF, new badges etc.