The following two paragraphs come from the eBay Seller's Description of the 911 RSR external oil tank featured in this photo gallery:

An outstanding reproduction of the 73' RSR External Oil-Tank. I believe it was available for the 73' as well as the 74' RSR. This particular oil-tank is for the 1973 model year RSR https://pbase.com/slidevalve911rsr/image/52914057

For comparison purposes, I have also included photos of an excellent reproduction https://pbase.com/slidevalve911rsr/image/70040597 of the factory 1973 Porsche 911 RSR External Oil-Tank (the 1974 oil-tank is also available). The only difference between this part and the factory original is the placement of the oil-level sending-unit in the tank (which you can not really see once the tank is installed!) The sending-unit on the factory RSR oil-tank is more closely located to the center of the tank while the reproduction RSR tank shown in the photos below has the sending-unit closer to the edge. This placement decision was made due to the more time-consuming and costly procedures required to implement this minor reproduction detail.