Hi Yukonflyr,
I have the engine back and repaired. I sent it off Monday afternoon and it was on my doorstep today Wednesday! I have a fair bill to pay but it has been ;
 Rehoned sleeve.
 New piston
 New ring
 New rear race.

No labour has been charged. But of course I have had to pay postage and VAT (TAX). So the total bill came to about half the price of a new engine. I bought the engine on the internet so I don’t know what original condition it was in. The guy has returned all the old parts so I know it is not a con, the old ball race is in a terrible state. He has sent me a do’s and don’ts list about half of it in highlight pen!

So I have learnt my lesson the hard way.
I should use Straight fuel. One recommended has 9% EDL 6% Castor 85% Methanol.

My old pal who taught me to fly passed away last year and bequeathed ( Well I don’t think it was actually in his Will but you know what I mean!) all his old fuel.
I used it regardless of what it contained and some of it was really smokey. One bottle I have left is Straight 20% castor 80 Methanol. I think it is the high castor oil that has done the damage.
Also “do not leave the model in a horizontal position after use always store it in the vertical position tail down. This is to prevent acid which is formed after combustion attacking steel parts and causing the rear ball race failure”.Point two I ignored.
From now on I will use after run oil. Any Ideas what is the best oil to use Yukonflyr?

Sorry for the long reply.
Regards
Richard.