Andy,

Filing contacts is likely to take off a thin coating contact of contact material.

I use strips of card stock pulled between contacts as I hold them together. They will will come out with a black stripe.

I usually dampen the strips with alcohol at first. Then I pull dry strips through until they come out clean. I will

go through many strips. Paper is cheaper than new contacts!

If you have been filing contacts you may already have ruined them and they will need to be replaced.

Tom   N3CRK