Many thanks for the info all, even though as I suspected it was not what I was hoping to hear!
The oil I drained from the sump originally contained no metal particles - the pan was quite clean as I recall, though there was a slight sludgy residue. Much the same as I have previously found in my other merc boxes apart from the emulsified oil. I have not found any metal or other particles in any of the 20 odd litres I have drained from it.
I contacted the previous owner today and discovered that the new radiator was fitted the day I collected the car! When I agreed to buy the car the a/c was not working and he sent it in to the garage which has maintained it (at great expense to him!) for the last 2 years. He was told that the condenser was holed and the repair would cost him £230. He picked the car up from them just before I collected it. When he got the bill in it was for £450 and included the new radiator, with no explanation. He has not paid the bill and is waiting for them to account for the new rad. He is recontacting them tomorrow and should be able to give me the full service history for the last 2 years. He assures me that he had no problems with the trans at all and it certainly worked fine on my 30 mile test drive. He is a genuine sort of guy & I believe him. In fact the problems only occurred after I changed the oil, some 2200 miles ago now.
I will post again tomorrow when I have the full story.