Robin
I did a quick google images on search word protectoseal. Looking through the images, I found several photos similar to your can. A few of the searches led to G503, where one fellow actually got a hold of the company, who told him that style a can was in production from around 58 until the mid 60s if I recall correctly.
http://g503.com/forums/viewtopic.php?f=37&t=223487
We used to have prtotectoseal cans on issue with the M113s and others for oil cans. I can't say I have ever seen your style in service.