What was the rating of the LED driver?#update# so I've replaced the lamps with some mr16 leds. Replaced the transformer with a led driver. Now when the lights on it flickers. Take a lamp out and 2 out of 3 work fine.
Most of those MR16 bulbs are 5W so for 3 of them you would need at least a 15W driver. If you have a 10W driver then you can get ones around 2.6W and 3 of them would work then.