Try bks-tuning.com in Germany for the belly pan. I have had good experience with them sourcing OEM parts at great prices. Another option is Shokan.com ... they do a lot of Audi parts. Third option is audionlineparts.com .. always found the best dealer prices there.

in terms of transmission fluid .. Audi says lifetime but I changed mine at 57k.. contact Brian at BND. Lot of folks here use his engine oil and transmission fluid.