I'm sure I seen a good guide on here for doing this but I can't for the life of me find it. Want to buy fluid but it's not cheap so want to get the right amount.

Anyone know of a good guide or even how much fluid I'll need to buy?

It's easy to do if you car has a trans cooler fitted.

I think from memory the there is a plastic cover under the bumper you can remove to get access to the lines by the transmission cooler on an EL

Disconnect the transmission cooler up at the front of the car under the bumper. Get an empty container such as a 5L oil container and put the flexible hose into it. Get some more hose and attached it to where the line attaches so both ends go into the container. This will catch all the oil and it won't matter if its the return or feed line. Only about 5L of oil will come out, the rest remains in the torque converter.

Start the car and it will drain the oil from the transmission; turn the car off as soon as the oil stops coming through. Just let it idle as there is no need to rev it as it only running the transmission pump.

Disconnect the other line into the cooler and use compressed air to empty the remaining oil in the transmission cooler; it won't take much pressure to drain the cooler.

You can now drop the pan and replace the transmission filter and seal. There will still be a bit of oil in the pan and it can be messy

You will need about 5-6 litres of oil to top it up again afterwards using this method. If you don't put enough oil in the car will slip in drive and not change gears properly and you don't want to over fill it either but a extra half a litre won't hurt.

You will need a hand pump to put the oil back in the trans. It's a b**ch to do.

Make sure the ATF is suitable for use in the BTR transmissions if it's not don't use it.

Looks good mate, will get a hold of a hand pump and get it sorted