Piston/Cylinder Wear Question (with pics)

[gascadia]

First I'm new to dirt biking and also gasgas, and I have to say this forum is amazing! I've already learned so much here, and I've only been reading for a few weeks.

Anyway, I bought a 2013 xc200R about a month ago, and I simply love it. I'm the 3rd owner, so I've been going through everything to make sure it's all in good shape maintenance-wise. The previous owner used to race and had a few other bikes, all in excellent shape. So of course it was super clean, and came with records indicating the suspension was revalved, and has the RB carb divider plate and circuit mods w/CEK needle and jetting. It also has the larger power valve cover from checkpoint offroad. The thing starts easily, runs great and makes plenty of power.

The guy I bought it from said he did the top end, all fluids and wheel bearings at 146 hours, but he reset the hour meter, so I have to take his word for it. Looked like a brand new hour meter with 8 hours on it at the time of purchase, and after a few test rides is now up to 16. After the last ride I pulled the pipe to inspect the piston, and wanted to get some opinions on wear from you guys who've worn and replaced many a piston.

Since this is my first bike I don't know much about reading early signs of wear, but I see more blow-by than I expected, and some small nicks, scratches & slight wear on the skirt. The cylinder still has crosshatching and the piston still has grooves from manufacturing.

Here are some photos of what I'm talking about.

Cylinder with crosshatch:

Cylinder 1.jpg

Rings:

Piston rings.jpg

Blow-by:

blowby.jpg

Middle of skirt:

skirt mid.JPG

Bottom of skirt:

skirt bottom.JPG

My main concern is the amount of blow-by for only 16 hours, and the little nicks along the skirt. Any thoughts on what might have caused this? Dirt making its way in through the intake perhaps? If this blow-by and wear is excessive for only 16 hours, I wonder if he might have put an A piston in this B cylinder. That could explain the blow-by. If others think this is not normal, I will pull the cylinder and measure everything. I'm looking at ordering a wossner "b" kit to have on hand for when the time comes (hopefully it's not now).

Thanks in advance!
Tristan