I know the opinion on using this d-limonene based cleaner vary greatly amoung model railroaders. This is true despite the fact that at least one company promotes it for their track cleaning cars.
On a recent visit to the home center, I discovered the subject pen. It is approximately the size of a marking pen. I purchased one and find it works well for removing small areas of "crud" from the rail heads.
The chiseled point can be easily slid along the rail head.
