Here's a couple of links:

Paddock Spares - Land Rover, Range Rover Parts & Accessories - Discovery, Defender and Freelander They're in the UK but will ship out parts. Check their prices (don't forget to add VAT at 17.5%) as they can be cheaper than Australia.

FWD Motors Pty Ltd Local outfit in Brisbane. Talk to Mark, he's helpful. If you're a club member you might get a discount. FWD sell both genuine and aftermarket parts, including filters.

Coopers or Britpart filters are both good. I believe that both supply to Land Rover in the LR livery - same filters.

Re tyre pressures, I run Michelin 750R16 tyres at 30psi regardless of load - and I'm heavily loaded when travelling. With the varied information listed I'd suggest a chalk test with your usual loading. Chalk a rectangular patch of tread and run the car over a clean bit of concrete or wood. The chalk should transfer evenly. If it's a small patch in the middle of the tread transfers, reduce the pressure, too much on the outside, increase the pressure.

As to the leak, I've been trying to locate one for the last four years. Still can't cure it though. Welcome to the world of Land Rovers.