'85 ATC 250R - Should I replace the top end?

I just walked in from the garage where I currently have the head off of my '85 ATC 250R. I took the head off because I notice a small coolant leak coming from the back of the head when I really had the throttle pinned. I was going to just replace the head gasket but now I'm not sure if I should just go all the way.

The top of the piston is black with a lot of carbon deposit on it. There are relatively large flakes laying on top of the piston. I believe it is due to the last owner because he ran it at 20:1 with a synthetic oil which in my opinion is way too rich. I further believe this because the plug that was in the bike when I bought it was black and oily. I then changed the mix ratio and jetting and the plugs are now cocoa brown.

The question is, should I put in a new piston/rings? Should I also bore the cylinder to make sure I have a good fresh cylinder?

Opinions would be greatly appreciated!

lol,if it has never been apart im sure it would be a good idea,did you happen to do a compression test?these two things play a major factor,especialy the first one.....lol

I haven't had it apart yet because I only own it for 2 months.

The guy before me rebuilt it about 1.5 years ago.

I didn't compression test it because I didn't intend to even consider a rebuild. I only intended to put a new head gasket on.

If the motor felt ok before ,i would put a new gasket in and do a compresion test to see where she's at.If your happy with it and its ok then put some more hours on it and when its time to tear down get a good port job when you do the top end,you will be happy. By the way what kind of head gasket was in there?