KSC G18c problem

[twsmith]

I just bought a new G18C and have found that it seems to fire fine in semi-auto, but the selector occasionally slips out of position after a few shots. In full auto it fires 3 shots before it slips out of position.

It is clean and well-lubed, but I've been using Green gas as I plan on upgrading if/when the plastic slide breaks. I don't think the gas is the problem as I tried just moving the slide back and forth it feels like something is catching slightly and it slowly moves the selector out of position, but I don't see any obvious rub points.

Any suggestions?

Thanks.

Wayne