The lid is floppy because the spring has lost some of its mojo. It seems like one could tap out the pin it swings on, replace with a new spring, and put it all back together. Anybody done this?
The issue could be finding the proper spring--or rebending (and / or retempering that spring. I wonder how it got "stretched"? The new spring should be 316 stainless steel. Do you know the brand of the deck pipe ?
Attwood, Perko, Suncor, Whitecap, Sea Dog, West Marine and some Chinese knok offs make deck pipes.