Hi Gidget,
The correct engine oil for the TD5 is one that's not easily obtained. You can't walk into Repco, Bursons or KMart to find Castrol Softec TXT 5W-30 sitting on the shelves. That's coz it only comes in a 20 litre can.
I rang up Castrol Australia and ordered 2 of these cans (free delivery if you order two) and paid $340 for the lot, from memory. They shipped it the very next day to my front door.
I didn't buy the oil because I have a TD5 but because my 2nd car is a BMW, and this is the only factory oil that is approved by BMW Australia for the current crop of petrol engines.
It's a synthetic oil that lasts a LONG time. You can expect 20,000 kms out of this oil in your TD5 if you do a lot of highway driving, but if you drive it offroad a lot or in lots of stop start traffic, I'd recommend an oil change at 10,000 or 15,000 km intervals instead.
WRT diff oils, I just use EP90 gear oil. I buy it from Penrite, because it's Australian and high quality. There's a mineral version and a fully synthetic version. Take your pick.
Lawrance Lee