[RonBee]

My opinion:

You need to avoid introducing the subject too abruptly. I suggest:
"Unfortunately, there continue to be problems with _______. It is my unfortunate duty to inform you that the __________ continues to arrive stained." Also, I hope you are going to be more specific than "equipment". Surely, the equipment in question has a name. Use that name.

The rest:

"The boxes are stained with the grease, and they are shipped to our customer in the USA. We have been penalised for this fault several times in the past; with penalty fees and shipment of new boxes. I am quite surprised by the repetition of such instances at your end. I ask you to look into this and suggest or take action to avoid such things from happening again in future. Your prompt reply on the matter would be appreciated.

What do you think?