Up for sale here is this set of 2 NOS vintage Dual parts, one #213966 shim and one #213968 tension spring. These are NOS unused and are guaranteed to work great for you. If the part number matches the part number in the service manual (which you can find free online), then this is the part for you. These came from a closed repair shop and are in good usable condition, though the spring probably has some light rust that won't affect operation. The paper bag is pictured but is not included.
All of my Dual parts are listed, and can be found by searching my other listings for "Dual." If you don't see it listed, I don't have it. Unfortunately I am not a turntable expert and can't provide any tech support for these.
US shipping and handling is $6, and international is $20, no matter what quantity you buy. All my small parts are set up for combined shipping, so just use the "add to cart" feature and then check out all at once, and it will combine shipping. If you have any questions, please ask.
I have many more Dual parts and other vintage electronics listed--feel free to take a look!