thanks for the responses chaps, and the suggestions. It appears that the pipe is available, having called a different Lexus dealer and given the same description. I then sent photos to both dealers who confirm it is available. I pick it up on Wednesday, although it is fairly extortionate at around £70, plus fitting charge and recharge of the system.
I took a look last night after dark with my UV torch and there are traces of the dye used elsewhere, but I don't know if they are transfer or old leaks ( I had my independent change some seals previously). I'm hoping the condensor is not leaking but my only option is to replace the pipe, recharge and see where we gp from there.
Whether you have had problems with your aircon or not, I would recommend taking out the battery tray and checking underneath for corrosion. I found some surface corrosion only and have treated it with Finnegans number one, which will kill it dead and protect it, although I will paint it again with hammerite. A few years left left alone, as it is out of sight, may have been a problem. I do wonder whether water can collect there, or perhaps a little battery acid has leaked, removing some paint