I have an "S"-plate car which has the separate transmission oil-to-air cooler between the aircon matrix and the main radiator, so I'm assuming that they changed about then.
All of the stainless vee-type coolers are very robust - I've yet to see one leaking.
The main oil-relasted problem is that the mass coolant temperature is a bit high in the 54degree engine, allowing the oil to run hot as they share the same coolant. If you have some tuning in mind, then I'd look to improvements to the coolant temperature first and oil temperature second.
To get the best of both worlds, you'd leave the vee-cooler in place and supplant it with an auxiliary oil-to-air cooler, for which the transmission one would be ideal PROVIDED IT CAN TAKE THE PRESSURE. Youi'll get the benefits of fast oil warming and ultimately low oil temperature, too.
I have run Omega B with a separate oil-to-air cooler in the front bumper. The only difficult part was routing the hoses from the back of the block (by the filter) around to the bumper - and this was on a car that had already had an aircon-ectomy. I still have the hoses if you want them.Tell you what, I'm coming past Rotherham tomorrow evening, so I'll put them in the car for you. You must ring me tho, as I won't see any e-mail between now and then.