Here is a used pitted original Porsche cupped washer 901.305.311.00 as used for both the transmission and motor mounts on 1965-89 911/912/912E/930 models. Wir sprechen Porsche! This is our best quality washer.
If you want to install RS mounts on your 911, you will need the right cupped washers. These are the ticket and I prefer the black over the plated (gold). Shipped quick and you get the cool little "901" sticker too!