One side on my 2000 C280 broke also, metal fatigue. IIRC it broke on the arm part not the fender.

Since there are plenty of holes around there, I fashioned an extension to the spring, a short piece of STIFF wire with hooks on both ends. You need to experiment a bit to get the right bends so it doesn't unhook itself when you close the lid. Be careful here! Also on my first try I didn't have it hooked in the right place and this resulted in an annoying rattle but my second try is working just fine.

glenmore
1991 300CE
2000 C280