I don't suppose this post will help you much but my partners car (peugeot 206 Auto 56K miles) has the very same problem, works fine cold but slips when hot. It used to work fine but then one day it appeared 'slip out of gear' particularly on bends. So I checked the fluid level and topped up but then it started to happen again. Checked the level and found in just a few miles a lot of fluid had disappeared. Couldn't see the source of the leak but noticed the undercarriage and rear bumper was coated in a mist of fluid. Thought then that the leak is obviously only happening when vehicle is in motion (hence no real puddle on driveway). Traced the problem to one of the diff/box output shaft oil seals (FWD). First thing to do then was drain existing fluid at which time I found a lot of water came out first, then fluid oil!. Realised then that the water and oil seal deterioration was the result of having to drive through lots of flood water in previous months. Don't do this with auto tx! Ok so then replaced the seals and filled with fresh fluid. Problem appeared to go away having driven 8 miles to town then back. All was well until just outside the house when all gears just slipped and would not return when really hot. Pushed car onto driveway and noticed the engine/tx smelled really hot. Checked level and found it was fine (no leaks). Conclusion is that either tx or torque convertor are damaged from the previous low fluid and/or water ingress or, the convertor still has a lot of water in it because most of the liquid in it wont drain when draining tx. Only solution is to pull out convertor. Its still waiting for that.