Brand new piston and Sleeve. The slime/gunk is from Castor re-forming. Castor provides Superior protection when used in 2-cycle applications due to the fact that when it is brought under extreme pressure (generated by friction/ or by extreme heat) its molecules reform/transform/combine into larger ones there by keeping expanding parts from making contact with each other. The draw back is the residue that becomes baked onto the hot spots. So based on this slime issue; yes you have excessive pinch and the engine is being run rich enough that your not "Baking the Castor" but getting close.
So maybe the guy running the synchronizer sneezed and in the process knocked over a couple of p.s. sets and the pistons fell out of there respective sleeves. Being that he is paid "piece work" he put back together which ever one was closest to the other. Somewhere out there, there is a person who just replaced his piston and sleeve. 1 gallon threw there engine its worn out.
You have not mentioned the manufacture? I have a piston and sleeve new in the bag that has never been opened. The reason is the piston is past the top of the sleeve to the point that the entire wrist pin bore is visible. Took pictures and called the importer...Sorry for the book.