If I'm not mistaken, you probably have a type of RCA jack in which the outer ground is a "sleeve" that snaps in place. I once had an amp that used these and they would come out if your cables were too tight.
If I'm right - the easiest fix is to find some spares outer sleeves. It's possible you may be able to find this type of RCA jack and radio shack, but I doubt it. You'll probably need to cannibalize them off of a similar receiver or other component from the Receiver's manufacturer. Shop Craig's list and local thrift shops for a parts unit.
Another option is to cannibalize them off the same receiver. I can't recall ever using all RCA inputs on any receiver or preamp I've owned (except on that only had 2 inputs. So, if you have 2 different inputs each missing one sleeve, pull one out from one and install it in the other. You may want to add a dab of superglue when you install it so it doesn't pull out every time you remove cables.
If I'm right - the easiest fix is to find some spares outer sleeves. It's possible you may be able to find this type of RCA jack and radio shack, but I doubt it. You'll probably need to cannibalize them off of a similar receiver or other component from the Receiver's manufacturer. Shop Craig's list and local thrift shops for a parts unit.
Another option is to cannibalize them off the same receiver. I can't recall ever using all RCA inputs on any receiver or preamp I've owned (except on that only had 2 inputs. So, if you have 2 different inputs each missing one sleeve, pull one out from one and install it in the other. You may want to add a dab of superglue when you install it so it doesn't pull out every time you remove cables.