I took my iffey DMU Motor to my mate's on Monday and he was able to get the old motor out (He was a bit more forceful than I ) and we got the new motor in, the DMU Runs really well now, very smooth indeed. I recently bought another middle trailer, so ran it as a 4 carriage train and it was fine, going backwards and forwards.

Now I have to sort out a similar problem on a GWR County Loco with motor in the tender behind.
Thank you for all your tips and suggestions, Steve.