So going to get a re-bore on my 2002 DT 125 R, just need advice on what others have used and on what not to buy, Cheers 

Make your own choice buy on the TDR250 forum, here and probably most other 2stroke forums Mitaka pistons are best value/performance. There are better but you pay for em.

Secondly no matter what anybody tells you a genuine head gasket is a MUST HAVE. Dont get a pattern one they leak. Gauranteed.

I reccomend stripping and cleaning the power valve too.

Cheers Cynic was leaning towards Mitaki Piston just wanted to cast the net for opinions ,Will strip power valve for sure.