told me all about the bike and its past,i took off both barrels today bottom barrel mint,top barrel had rubbed piston skirt to barrel. so i have cleaned the barrel with a scotchbrite,removed all alloy from barrel,and luckly when i brought the bike i got 2 spare pistons that came from those barrels, i was going to put just one in but when i weighed the pistons and pins etc there was 10g difference so am going to put pair in, 
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NSR250 MC18