XK8 transmission oil cooler leak

[smucker1]

Hi, hoping someone can enlighten me.
I have a leak on the transmission oil cooler pipe that goes into the lower connection on the main radiator. The leak is on the engine side of the nut/union. My mechanic had a quick look today and recons it is an O-ring that has failed, I happen to agree. So I spoke to Jaguar and no O-rings are listed for my car (2004 4.2 XK8) but are for the older models. They suggested I take the nut off and bring the O-ring in and they will "size it up". My fear is loads of trans oil will escape if I remove this pipe. Then I will need to top up the transmission with fresh oil.
Does anyone have any knowledge of this problem / part? Thanks in advance.

[wack]

If it's a similar pipe to the one on my 4.0 XK8 it'll be an alloy thread, chances are it'll strip the thread off as you try and undo it so go carefully, you will lose some fluid it's unavoidable