"Going Spare" you were so right; sometime ago when I had this fault, I put the loco back in it's box wanting to forget about it. I couldn't sell it as my youngest daughter bought it for me for Xmas. Yesterday I took it out of the box and had a good look at it. I gave it a bit of a service and it ran better but not perfect, cleaning the wheels I noticed that one of the engine tyres was missing, so this could have been one of the things that stopped the loco running properly and slow speeds around 2nd radius curves. I do feel a bit of an idiot writing first without checking the tender drive, this has taught me not to go from long term memory, but look first and then ask. But thank you for answering my dilemma.