LJ have found that halfords do a small black car interior trim clip that works perfectly as a replacement screw for eggs
It looks like a black screw and rawlplug- when you screw in the screw it expands the plug- have replaced both my lid screws on both hoppers with these.
Benefits
Loads in packet for spares
Works perfectly
Doesn't have any sharp edges on inside of hopper
Easy to remove and re-insert for cleaning
Doesn't damage lid
Disadvantages
Very slightly less friction than the screws- i have used a singular spring and have had no problems with lids opening or spilling
Hope that helps
A.B