I have 13 marelon seacocks. They suggest using salad oil to lube them. I rarely do. They all work well. I have replaced some of them with the flanged seacock version but most are the standard ball valve type. The worst failure I have ever had with them is not sealing 100%. Never a catastrophic failure.

Bronze is vulnerable to electrolysis. Bronze plug type seacocks will seize up and have to be disassembled and lapped.

Marelon plastic is inert and worry free.

A big problem with bronze is getting the old ones out. The seacocks seize to the thruhull and have to be ground/cut out.